Data's cat, Spot, is referred to as 'he' in the earlier series. However, in series seven the same cat has babies. [When Spot has her kittens Data says to someone. "She is not a he after all". Even Data makes mistakes.]

The Enterprise has an automatic fire extinguishing system, utilized in "Up the Long Ladder", but apparently is very selective when it want to put fires out. It never puts out fires in many other episodes, be it a fire from a candle (Firstborn), a bonfire (Masks), or an out of control fire (Masks), just to name a few. [If a person has a need or a desire to disable the fire suppression system they can do. The Candles feature alot in Klingon culture & as such Worf uses them alot, other people on the ship could also use them for their religious ceremonies & as the Federation is a great believer in all sorts of freedoms & personal expressions they let people celebrate things how they want as long as it doesn't endanger people. The fire suppression system (like other systems on the ship) is also prone to damage & invasion by other, older computer programes (remember "Contagion") which could stop it from operating]

Anytime the crew is faced with a person that claims to be a time traveller or a crew member acts different and claims it's from time displacement the rest of the crew's first response is skepticism. Why? On average, the Enterprise gang deals with time travel once or twice a month. One would think the logical response would be to say "OK, someone grab a tricorder and lets scan for time travel events." This is especially evident in the series finale. [Let's start with the time travellers and time displacements that happen on the ship, excluding the final episode. I can't think of a single example were the individual wasn't believed (with a little proof), outside of the episode dealing with Worf and quantum realities. But there, he wasn't traveling through time, but through different realities and he thought he was going crazy. Travellers and displacments off the ship: It isn't a simple tricoder scan that tells them about the time displacments. They need deep medical scans, something the tricoder is unable to provide. The series finale: Picard didn't reveal to the past Enterprise about his time shifts: He didn't want to pollute the time line. He informed the present Enterprise and they began to look for proof that it happened. He informed the future crew and they disbelieved because of his degenerative disease. His *** syndrome had effects on the brain including psycosis. The future believed that it was his disease taking full effect.] Corrected by Rlvlk

Throughout the Star Trek series, when there is a medical emergency or a security situation, why don't they use the site to site transporters to get people to where they need to be? Seconds matter in an emergency but they take the time to move injured people via the corridors. [Site-to-site transports require a great deal of power, so are only used in absolute emergencies. Generally speaking, if there are injuries on board, the Enterprise would almost certainly have taken damage and will probably be in an alert status, where power will be required for the primary systems like the shields, engines and weapons. As such, the necessary power to perform site-to-site transports would not be made available except in cases of the utmost urgency.] Corrected by Tailkinker

Throughout the entire Star Trek series, space explosions, weapons fire, ship engines, etc. can be heard in many shots originating in space. However, in space there is no sound. These events should be silent. [True, but this mistake is true for virtually all sci-fi movies and tv shows, so producers need to be given creative license in this area for dramatic effect.]

Even though living matter, especially complex living matter, cannot be created and taken out of the holodeck, the ship's replicators can create food which includes meat, salad, etc. [That's because there is real food here (bland and tasteless, yet nutritious) that has only been disguised as another food which the consumer would enjoy more. The signals which disguise the foods' appearance also send impulses to your brain, which trick it into thinking that what you're eating not only looks; but also smells, feels, and tastes like meat or salad or whatever.] Corrected by Phixius

The model of the Enterprise in Raymond's quarters has the warp nacelles on backwards. [When in the episode is the model described as being of the Enterprise? Not an error.] Corrected by John W Rosa

At the end of the scene where Admiral Quinn is first walking around the Enterprise with Picard and Riker, a male crew member can be seen wearing a female officer's dress uniform. [Not a mistake. That was a normal uniform variation at that point in the show. It wasn't seen a lot, but it was intentional- not a mistake.] Corrected by John W Rosa

In the episode "Skin of Evil", right after Commander Riker gets pulled into the sludge type black substance watch the left side of the screen. When the away team looks into it after Riker's face comes out of the sludge you will see something plop into the goo, that was Geordi's phaser falling out of his holster when he leaned over the pool of goo. [Not a mistake, as it is possible to lose things like this in real life. The mistake is, however, that the phaser reappears later, which is already listed on this site.] Corrected by Twotall

Geordi's phaser falls out when the away team moves to help Riker and gets sand on it. After Picard beams down it's back in Geordi's holster, clean and shiny. [It was several minutes before Picard beamed down, more than enough time for Geordi to pick up his phaser and dust it off.]

When Riker is dragged into the pool of goo, his head reappears for just a moment, then is pulled back into the pool. Note that his mouth is open and fills with goo, but his mouth is above the surface. Obviously this is a mask that is pulled under. [The pool of goo is a living, shape shifting entity called Armus. If Armus wanted to only partially fill Riker's mouth with some of himself, it surely would have been in his power.] Corrected by Rlvlk

When starting the warp-core the matter / antimatter is injected in the ratio 25:1. Four episodes earlier (S01-18, Coming of age) Wesley solves the trick question at the Starfleet entrance exam with the only solution : The ratio has to be 1:1. [Is this the proper ratio for a Galaxy class or a generic warp core? 1701-D is Starfleet's newest, most advanced vessel. It's possible that her core uses a different procedure for start up. Also, academies historically use older equipment for training purposes, since the state of the art is "on the front lines", making it even more likely that procedures on Enterprise are different from those in other vessels.] Corrected by Grumpy Scot

The Klingon Korris makes reference to the Klingons' homeworld as "Kling." - "I refuse to let the traitors of Kling pick the meat from my bones." This is the first and only time the Klingon home planet is called "Kling" - it is later "officially" named Qo'noS in the sixth Star Trek movie. [it's generally thought that Kling is a district or city on Qo'nos.] [They actually say "Kli", not "Kling". It's like "Earth" and "Terra" - two names for the same planet. But if you analyse the word klingon, the litteral translation to english is "inhabitant of Kli". With this same rule, humans (terrans) are called "terrangans" in the klingan english dictionary.]

Jake Kurland is described as a skilled shuttle operator, yet he still manages to unbalance the shuttle's engines. [Licensed surgeons (whom we can assume are 'skilled' based on their schooling and licensing) have been known to leave surgical instruments inside patients. Pobody is nerfect. Not a 'mistake' or 'plot hole'.] Corrected by John W Rosa

The Aldeans offer to provide the Federation with extensive scientific knowledge in exchange for children, because the Aldeans are barren. Troi, Crusher, and Riker reject this offer immediately, and the Aldenas kidnap seven children from the Enterprise. It's totally understandable that the crew of the Enterprise would be unwilling to part with their children. But are there not any human or humanoid children living as underpriveliged orphans, either in the Federation or under the awareness thereof? Surely there are many children who would benefit greatly from being raised on Aldea, even though no such children were on the Enterprise. The Dominion war and the Cardassian occupation of Bajor orphaned thousands. And surely, if given a choice, at least some of these children would choose to live in a place with new parents who would love and pamper them, thus avoiding any moral dilemmas. [That would be selling children: slavery. Giving children in exchange for scientific knowledge is the selling a person. The Federation cannot interfere in the societies of non-federation planets: The prime directive. They cannot simply take Bajoran war orphans and take them to Aldea. And even if they could, no society would exchange their orphans for the knowledge, see above reason. The Aldeans are unable to have children because their planetary cloaking device has rendered it impossible for them to have children. It sterilized them. They will no longer use the cloaking device for this reason. It would doom any child brought to their planet to the same fate. That is why they gave the kids back instead of fighting. The cloak will no longer be used: therefore, the planet's location will no longer be secret. Since it will no longer be secret, families will be able to immigrate to the planet and the Aldeans can teach them.] Corrected by Rlvlk

With such advanced technology, the Aldeans should've known the effects to the ozone layer their device has. [With our non-advanced technology, we should know what effect we're having on our environment, but we seem to be doing a pretty good job of being in denial about it.] Corrected by Myridon

During the 'little power demonstration' a repulser beam hits the Enterprise and throw it three days away from the planet. But no-one on the bridge shows any signs of movement - even the standing one. Remember every space battle when after each hit you see people flying through the air . [Since the Enterprise has artificial gravity and inertial compensators, the crew is usually unaffected by changes in speed or trajectory - no one is slammed to the back walls when they go to warp, for instance. These systems are often affected as power is rerouted to shields during a battle. The momentary readjustment results in crewmembers falling or flying. Clearly, these systems weren't affected by the repulser beam.] Corrected by JC Fernandez

At the end of the episode the Enterprise heads off to ward off Romulan Warbirds, but according to "The Neutral Zone" the Romulans haven't been heard of since the "Tomed Incident." [The Enterprise simply could have been responding to a false alarm at the end of this episode.]

Riker locks a tractor beam on the Stargazer with its shields up, even though it is established TNG-era tractor beams can't do that. [It has also been established that as time passes in the TNG universe, new technology allows them to overcome older technology. For example, they are unable to beam through shields, but in several episodes they manage to do it anyway because of inferior/flawed technology. Remember, the Stargazer is an old ship and its shield technology is outdated.]

Riker refers to Bok as captain, when in fact the commanding officer on a Ferengi vessel is Daimon. [True, but Daimon is the Ferengi equivalent of a Starfleet Captain.] Corrected by Cubs Fan