Continuity mistake: After the T. Rex escapes its paddock and is drawn to the light Lex is holding, when the T. Rex begins to roar in the shots from inside Explorer 4 there's a Jurassic Park sticker adhered to the windshield (not the ID tag hanging from rear-view mirror), that wasn't there before.
Continuity mistake: When the five characters start to leave the helicopter upon arrival on the island, Richard Attenborough is not sitting opposite Jeff Goldblum as he was moments earlier as the helicopter descended to the pad.
Factual error: At the beginning of the film we are shown an amber mine in the Dominican Republic. This amber is only 45 million years old, Hammond would never bother buying the amber from there as dinosaurs disappeared from the fossil record 65 million years ago.
Character mistake: When Genarro is explaining to Hammond that he is at the park to report Hammond's progress to the investors, he says "In 48 hours if they're not impressed, I'm not impressed. We'll shut you down, John." He should have said "If I'm not impressed, they're not impressed" since the investors would be shutting down the park on his advice, not the other way around.