Factual error: A copy of Miles Davis' album "Tutu" is sitting on a counter. Odd since the recording wasn't made until 1986.
Continuity mistake: When Marge gets out of the water and climbs the stairs on the sailboat her swimsuit is blue. But when she is on board and we get a close up it is red.
Visible crew/equipment: When Dickie and Ripley are scootering down a little Italian hillside, you can see the shadow of the whole film crew against the hill.
Factual error: When Dickie and Ripley go to the first jazzclub together and Dickie and the Italian singer invites Ripley to join them on stage, the microphone they're using is entirely misplaced. That type of microphone wasn't even on the market yet.
Factual error: In the scene in Venice where Marge is leaving on the boat with Dickie's father, there is a shot from Tom's point of view looking out onto the water. In the distance a modern crane can be seen on the left - something that the director Mingella himself points out on the DVD commentary.
Revealing mistake: When Ripley is leaving New York, there is the shot of the ship sailing out of the harbour. Check out the water - one layer has been 'cloned' on top of another.
Continuity mistake: During the opera intermission scene, when Tom first meets up with Marge and Peter, Peter's hair is neatly slicked back. In the next shot, his hair is hanging in his face a little. The next time he's shown, his hair is neat once more, and a moment later it's messy again.
Revealing mistake: During the scene on the boat while Ripley is reading the book, Paltrow gets out of the water and walks to where he is leaving a trail of wet footprints. If you notice there is already one set of footprints that have not dried from an earlier take.
Revealing mistake: In the scene in the club when Jude Law is playing the saxophone, you never actually see his fingers move while he's playing.
Continuity mistake: When Tom and Dickie enter the jazz club in Naples, Dickie's hat keeps appearing and disappearing from his head. (Within the film this is a matter of continuity and thus a mistake, regardless if there is an explanation on the music video.)
Factual error: The scene where they are in the cockpit of the sailboat shows StayLock rigging, which was not invented until the 80s.
Continuity mistake: When Tom, as Dickie, rents a place in Rome, and after Tom kills Freddie, the police are all over him. Marge comes calling and Tom, as Dickie, asks the policeman to ask her to come back later, which leaves Tom alone with the detective. But as we see Marge creeping up the stairs, to see Dickie, suddenly, the policeman is with Tom and the detective, even though the policeman had left and Tom had closed the doors, so the policeman should not have been there.
Continuity mistake: From the viewpoint of a boat behind Dickie's boat "The Bird", when Dickie gives the tiller to Freddie, so he can go below with Marge, there's hardly any wind, both sails are flapping around, but when we get the view from midships, the front sail, which was on the starboard side, is now, suddenly, on the port side and full of wind, no flapping around at all.
Visible crew/equipment: When Dickie, Tom and Marge are coming out of a hotel via some glass doors, the cameraman is visible when it closes.
Continuity mistake: A far ways into the film, when Gweneth Paltrow is leaving on the boat, Matt Damon is standing on the dock watching her leave. At one point, it cuts to a far shot showing him pulling his hair back with his hand, but then it shows a shot from behind, and his hands are down at his sides. It's not very likely he could move his hands that fast.
Continuity mistake: In the scene where Tom is analysing Dickie's handwriting, Tom is smoking a cigarette and is shown taking a puff. The camera suddenly cuts to behind Tom's head where he has moved his arm & the cigarette - there is not enough time for him to do so.
Revealing mistake: The letter which is typed on the Olivetti portable typewriter (certainly an accurate model for this period) is obviously a modern laser-printed letter, not from a manual typewriter.