A Colt revolver like the one Julie uses to shoot Ben Willis only holds six shots. Julie fires eight times and it misfires once, when Ray tries to shoot Ben Willis, making it hold nine bullets.
At the end there is a tombstone that says "Julie 1998" which is wrong because although the movie was released in 98 the actual characters should of been living in 1999 or later, because the beginning of part one takes place in 1997 (at the pageant they say it's 1997) then one yr later (98) the killer returns to seek revenge, part one ends... THEN it's at least 1-2 yrs later before part 2 takes place.
Ray's arm is broken after Ben tries running him over, but near the end of the film, both his arms are fully functional during his fist fight against Will.
After Ray's "accident" he walks down the street with his left arm in a sling. In the next scene and from then on it's his right arm that is in a sling.
(at around 11 mins) When at the club Julie is shown holding a stick with two cherries on it. Then when they return back to her to ask her to dance there are three.
A revolver used at the end of the movie holds 6 shots. If 1 was a dud, there should have been only 5 shots left available at most.
The title itself is a goof. The movie takes place one year later, so it should be: 'I Still Know What You Did the Summer Before Last'.
(at around 34 mins) At the bar, Nancy says, "What you guys want is a Dark and Stormy." She then lists the ingredients as "Vernon's rum, a little ginger beer, a splash of Tabasco". This is not a Dark 'N' Stormy. A Dark 'n' Stormy is a highball cocktail made with Gosling's Black Seal rum (the dark) and ginger beer (the stormy) served over ice and garnished with a slice of lime. The name "Dark N Stormy" and the corresponding recipe is a trademark of Gosling's Brothers Ltd.
When Willis pulls out his hook to kill someone, it makes the stereotypical sound of metal against metal. However, the hook would need to be sheathed to make such a sound; furthermore, a curved hook is unable to be sheathed to make such a sound.
(at around 46 mins) When Titus appears from underwater and scares Karla and Tyrell he lights up a joint which should be wet and then puts it in the water again when he swims away.
(at around 1h 2 mins) Julie keeps her eyes open for at least three minutes in the tanning bed, which can cause severe sight problems almost immediately.
(at around 1h 21 mins) When Karla falls through the glass roof, her back should be all lacerated.
(at around 59 mins) Just as Karla and Julie enter the room where the tanning bed is, Karla says, "Come on Julie it's better than a day at the beach girl," yet her mouth does not move until the next shot.
(at around 1h 5 mins) After Julia explains about what happened two summers ago and that she didn't want to drag anybody else into it. Karla mouths, "It's too late for that now," but all we actually hear is, "It's too late for that..."
Hills and rock formations reveal true filming location (Mexico), not the Bahamas.
There are significant amounts of Spanish architecture, which is not indigenous to the Bahamas.
They won the radio contest when they named Rio de Janeiro as the capital of Brazil. The capital of Brazil is Brasilia as of 1960.
As Julie and her group arrive, the hotel grounds are brimming with other guests. However, when they check in and encounter the hotel manager seconds later, and when Ben Willis arrives and starts killing, the hotel is totally deserted leaving us only with the main characters. Apart from the fact that all other hotel guests seem to have vanished in an instance, it also is highly implausible that even during 'off season' there wouldn't be at least a few guests left. Surely Ben Willis didn't just kill everybody off?
(at around 1h 4 mins) When the gang is on the dock, Tyrell says there's only one person unaccounted for - Estes. However, by this point, there are two people unaccounted for - Estes and Nancy.
(at around 1h 3 mins) Will and Tyrell resort to smashing the tanning bed open to let Julie escape, but surely they would simply have turned it off or unplugged the machine instead.
When Karla and Julie are going up to sing Karaoke you can hear Tryel call Karla, Brandy which is the actress's real name.