Revealing mistake: During the whole scene of the T-Rex attacking the Explorers you see an illumination that moves from place to place. Sometimes the illumination is in the deep woods, and then it is behind the dinosaur when it is next to the vehicle. When the T-Rex first walks up and sniffs Tim and Lex's Explorer you can even see the light to the left of Rex's head. Since the power is out, no lights are on except the vehicle headlights and they aren't making that much light. Also, there is no moonlight since it is pouring with rain. (00:58:00 - 01:07:00)
Continuity mistake: When the group are at the velociraptor paddock Hammond says "And that's why we're taking extreme precautions". Dr. Malcolm's head changes from looking sideways to being tilted down a lot more. Also Hammond starts to turn and then turns again in the following shot. (00:31:50)
Continuity mistake: As the T-Rex is looking for Lex and Dr. Grant, Dr. Grant says "Don't move. He can't see us if you don't move." When he says this he is to the left of the wheel arch. Then, the T-Rex blows the hat off Dr. Grant who, with Lex is at the end of the upturned 4x4 when the T-Rex knocks it but in the next shot they have moved and are not at the end of the 4x4. They are back where they started, to the left of the wheel. (01:05:30)
Factual error: When the goat leg falls down onto the glass roof of the tour vehicle, the wound on it is much too clean. Whether it is actual meat, it looks like it was cut with a knife. Dinosaurs, like crocodiles had conical teeth and had to tear or rip their prey apart - unlike cats or dogs, whose premolars act in a scissor-like way and actually cut the meat. The wound surface should be frayed and messy. Also, a T-Rex wouldn't even be able to tear apart a goat, because it's too small to step on it and tear at it at the same time. Instead, he would chew and shake it a few times to shatter the bones, then swallow it whole.
Character mistake: Hammond talks about all the things that went wrong when Disneyland opened in 1956. Disneyland actually opened in 1955. (01:32:10)
Continuity mistake: When the tyrannosaurus is crushing the upside down Landcruiser and mud begins to flow in through the side shattered windows, Lex and Tim are already completely muddy all the way from the tops of their heads, possibly from previous takes.
Continuity mistake: When Muldoon and Hammond are talking about the tropical storm the first time we see a shot of Nedry's workstation behind them and there's hardly anything on the floor, but a few minutes later when Hammond says their lives are in Nedry's hands suddenly the floor is covered in trash.
Deliberate mistake: At the end of the kitchen scene with the kids and the raptors, one of the raptors chases Tim as he runs to the door. As it's doing this, Tim is running away with a bad limp, then as the raptor gains speed and is close behind, Tim's legs are perfectly fine as he sprints out the door and shuts it. (01:47:05)
Revealing mistake: When Alan and Tim climb down the tree to escape from the falling car, you can see cables along the bark of the tree below the car as it falls. (01:14:20)
Character mistake: The correct spelling of stegosaurus is steg"o"saurus yet when Nedry steals the embryos, the freezer says steg"a"saurus. (00:55:50)
Continuity mistake: When Ellie runs away from Muldoon towards the Power Station, she climbs over a tree and watches a path in front with two more fallen trees on the way. When she is about to jump over the first one some branches suddenly appear on the close-up to help her do the jump. Furthermore, when she is about jump over the second tree the close-up is a repetition of the previous tree.