Revealing mistake: Two mistakes here: Before Darth Vader cuts Luke's hand, he cuts in half three columns. In the close-up, one can see that what held them together was a piece of wrinkled duct tape. In further shots, the tape disappears and only the scorched part of the column is visible.
Audio problem: When Luke says, "Now all we gotta do is find this Yoda, if he even exists," if you look closely, his mouth never moves.
Visible crew/equipment: A boom microphone is reflected in Luke's goggles when he says "Hey, what's the matter? You smell something?"
Continuity mistake: In the original 1980 version, in the first wideshot of Darth Vader's Star Destroyer, the light of a Star Destroyer can be seen on the right side just flying through space. This is fixed in the 2004 DVD release.
Revealing mistake: When Luke and Vader are fighting in Cloud City, there is something looking like tape wherever they hit something with their lightsabers. Maybe it's pyrotechnic charges?
Other mistake: In the original version, when the Rebel Transport ship leaves Hoth before the ion cannon is fired, an X-wing flies past it, and you can see the transport ship through one of its wings. This has been fixed in the Special Edition.
Continuity mistake: When Janson (Wedge's gunner) fires the harpoon at a leg of an AT-AT, in the first shot of the snowspeeder flying around the AT-AT, the speeder casts a shadow on the snow. In all other shots of this sequence, there is no shadow of the snowspeeder.
Revealing mistake: Right after Luke and Darth fight for the first time, Darth gets kicked off the Carbonite freezer. Then Luke jumps down to fight him again. After he jumps, you hear what sounds suspiciously like a trampoline. Then in the lower right screen, you can see Luke's head pop back up into frame. Widescreen Version only, although the sound is audible on the fullscreen version too.
Continuity mistake: When Luke leaves Dagobah, he uses a ladder to climb into his cockpit, but when he sits in, it has disappeared.
Revealing mistake: In the original (not Special Edition): When the AT-ATs are attacking the Hoth base, they do a camera angle from inside Luke's cockpit. As his snowspeeder is passing through the legs of an AT-AT, part of the cockpit becomes translucent and you can slightly see the AT-AT through a metal bar.
Continuity mistake: When the Millennium Falcon is being chased by the Empire after leaving Hoth, C-3PO's position in the cockpit keeps changing slightly between shots. At one point he falls towards Chewbacca (with both arms in that direction) but during the in-between cut to Leia, he is also still there (with his left arm extended her way).
Other mistake: In the ending credits, Denis Lawson's name is misspelled "Dennis." The filmmakers made the same mistake in "Star Wars."
Suggested correction: And in the Star Wars corrections page, you will find that mistake with the explanation that Lawson has used both Denis and Dennis in his career.
Continuity mistake: When they are escaping from the Hoth base, Chewbacca enters the Millennium Falcon but when Han and Leia enter some seconds later, Chewbacca is still going inside the spaceship.
Continuity mistake: At the fight between Luke and Darth Vader, after Luke pushes Vader to fall down from the top of the hibernating cabin, he looks down with the lighting light sabre in the hand. He goes back and we hear the switch-off sound of the light sabre, he comes back three meters left of the point he looked down and in his hand is the switched-off sabre. But as he goes back before this, we can see the end of the prop-light sabre taken out of Luke's hand and obviously the off-prop sabre is given in his hand.
Continuity mistake: When Yoda is teaching Luke, he is strapped to Luke's back in a rucksack. When Luke puts Yoda down, the little Jedi master is still inside the bag. Luke then reaches for his jacket, and in the next shot of Yoda, he has in a few seconds managed to get out the bag and is now sitting next to it. He is not even sitting in the same place as in the previous shot, and is also holding a walking stick he didn't have when Luke put him down.
Revealing mistake: In the shot where the Falcon is underneath the Star Destroyer, it is transparent and you can see the part of the Star Destroyer through it.
Revealing mistake: During the battle on Hoth, after Luke says: "Hobbie, you're still with me?", there's a shot of an AT-ST shooting at the rebel and after that, there a shot of an explosion behind them. You can see that the rebels are actually dummies in that shot.
Continuity mistake: After Luke places the thermal detonator inside an AT-AT, he falls to the ground. The AT-AT takes only one step before the charge goes off, but when the AT-AT explodes, it is much further away from Luke than one step.
Continuity mistake: In an exterior shot in Cloud City, Leia can be seen through the window of a building, with one hand on her hip and the other arm at her side. In the following interior shot, her hands are clasped together.
Visible crew/equipment: When Luke's X-Wing crashes into the swamp, the set lighting is visible along the edges of the swamp (most noticeable in the the first shot of him getting out of his ship in the original 1980 version of the film).