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.
Continuity mistake: When Sam Neill found the eggshells beside the root of the tree, they are on the dark soil. In the other shot, the same eggshells are on the clear sand.
Revealing mistake: When Ellie runs from the Raptor the stunt double who runs for her has on a wig that looks nothing like her real hair. It just looks very fake.
Continuity mistake: When Dennis tries to get the dinosaur to fetch a stick, at first the stick is perfectly straight. Then they show a shot of Dennis from the front, and all of a sudden the stick is crooked.
Continuity mistake: When Grant shoots at the window in the control room, and we see the holes, they are holes from rifle bullets. But the shell casings on the floor is from a shotgun. And yes - shotgun shells do exist with one big slug in them, but then the holes in the glass would be a lot bigger.
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: 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.
Continuity mistake: When the T-Rex has come and nearly destroyed the car, Grant is trying to get Tim and Lex out of the car. Lex then screams and this causes Grant to turn around and cover her mouth. They are sitting on one side of a tyre on the car when Grant has his hat on. In the next shot (when the T-Rex has blown Grant's hat off) they are on the other side of the tyre.
Continuity mistake: Just as they start going down the wire into the T-Rex paddock, in addition to the problem mentioned above with the ground level suddenly dropping, take a look at the wire. In the first shot underneath them it's curling up and towards the camera, like it's caught on something, then it changes angle, and the wire's hanging straight down.