Continuity mistake: During the opening sequence a couple shots show it raining where other shots have no rain and a dry environment. First noticed after Muldoon says "Jophery raise the gate" and when the gatekeeper falls off the transport box.
Continuity mistake: When they first land on the island, the actors' positions change. In the interior shots, Satler is sitting to Hammond's left during the descent. When the copter door opens, Hammond is on the other side, his left side facing the door. They would not have switched places during the descent.
Revealing mistake: When the Explorers are entering the park through the large wooden gate, during the overhead angle you can see that the perimeter fence isn't continuous.
Revealing mistake: In the shot immediately following Ellie turning on the circuit breakers when the raptor attacks her, we see a light bulb touching its head. There is smoke appearing where the bulb is in contact with the raptors head, the power has been off for a while the bulb would not be that hot after being on for just a few seconds.
Continuity mistake: Hammond pours champagne into his glass and it's full of foam. After Grant says his line, when Hammond says, "...for the next three years." the foam is all gone. Foam from champagne takes longer to disappear.
Revealing mistake: In the kitchen sequence when Lex almost falls from the hole in the ceiling, she looks straight back up at the camera. Rather than cut away from the stunt double at this point, they actually bothered to CGI the actress' face over the top so they could use the sequence right through. Unfortunately you can tell what's been done.
Revealing mistake: During the external shot of Nedry getting attacked by the dilophosaurus, there is a clear reflection of stage lights near the jeep's front left wheel.
Continuity mistake: Right before Lex and Tim scream when the T-Rex roars at them Lex is holding a flashlight, in the first shot you can see that Lex is staying completely still with the flashlight facing towards the driver seat but in the next shot you can see that it is pointing out the passenger side window.
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.
Continuity mistake: After being electrocuted, Tim flies down vertically, but Dr. Grant catches him horizontally.
Continuity mistake: When Nedry is trying out the shaving foam can, he puts some on his right hand. When the camera pans back after he's wiped most of it off on the pie, his hand is suddenly completely clean. He then pretends to wipe it off with a napkin anyway.
Continuity mistake: When the T-rex is attacking the vehicle with the kids inside, Alan gets out of the other car. Even though it is pouring rain and Alan is standing perfectly still, no raindrops are seen hitting his solid, medium-colored shirt. It stays perfectly dry, even though there is nothing overhead that is shielding him from the rain. It is only after the scene cuts to him at the other car that the shirt is suddenly drenched. The rain is obviously CGI.
Factual error: The way the car "slides" down the tree as Grant and Tim are climbing down is very unrealistic. Rather than hugging the trunk like it does, the branches (some of which are thick enough) would deflect it away from the trunk.