Audio problem: When Luke and Vader are fighting in the carbon freezing room, at one point Luke forces Vader off the side, looks around, then jump down himself to look for Vader. Listen to the sound that is supposed to be the sound of Luke's feet hitting the ground; you can see Luke stand back up after jumping over the side in the bottom left corner of the screen, but Luke is almost full stood back up when we hear the sound of his feet hitting the ground.
Continuity mistake: When Vader is seen in Cloud City, Lando says, "I had no choice, they arrived right before you did" and two of the stormtroopers on the lowest step are standing about a metre apart. In the following close-up of Lando, they are standing so close together that their ankles are touching. This can only be seen in the widescreen version. (01:25:05)
Continuity mistake: When the Millennium Falcon is approaching Cloud City, Leia's hand is on the top of Han's pilot seat. In some shots, her hand is in the middle of the seat, in other shots, it is right next to the middle.
Continuity mistake: When a blast rocks the command centre during the battle on Hoth, C-3PO is thrown backwards into Han's arms. As the wideshot leaves, Threepio is leaning backwards, supported by Han, but in the next shot, both of them standing upright in a normal way. Toryn Farr, the woman sitting behind them, has changed position as well. (00:30:40)
Continuity mistake: When Chewbacca is choking Lando, as Leia says, "We don't need any of your help.", Lando is standing on his knees. In the next shot, only his head can be seen, but the position of his head and Chewie's arms shows that he is now standing straight up. In the next shot, he is on his knees again. (01:38:15)
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).
Audio problem: In the carbon freezing chamber, Han says to Chewbacca, "The Princess - you have to take care of her". When he says, "You have to take care of her", his head is shown from behind, but the motion of his jaw doesn't match the words.
Continuity mistake: In the shot before Luke's hand is cut off, his left arm is bent and his elbow is positioned next to a pole. In the next shot, his arm is straight and his elbow is next to a different pole. Also, his lightsaber is held in a different angle. This is best seen in the widescreen version. (01:45:55)