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: As Major Derlin and another Rebel officer talk before the shield doors are closed, another officer walks under the starship Leia's standing by. In the next shot, he's gone. (00:11:30)
Continuity mistake: When the Millennium Falcon is pursued by the Star Destroyers after escaping the space slug and, Han pulls the lever for the hyperdrive. In the next shot from behind, the lever has not been pulled.
Continuity mistake: After the Millennium Falcon has left Hoth and Han is trying to repair the hyperdrive, in the shot after he asks for alluvial dampers, the tool box Chewbacca gives him can be seen in the lower left hand corner. When Chewie takes the box, it is lying in a different position than in the previous shot. As Chewie walks over to Han, he is holding the right side of the box with his right hand, but as he puts it down, he is holding the left side of the box with his left hand. There are also more tools in the box than in the previous shot.
Other mistake: When the Millennium Falcon escapes Hoth and is pursued by the Star Destroyers, frantic movements cause them to collide. Watch the interior shot of the Star Destroyer as everybody is thrown around. Near the bottom of the screen one of the computer consoles comes away from the wall and is hurridly pushed back into place by a controller! (00:35:55)
Continuity mistake: When Leia briefs a group of Rebel pilots in the hangar on Hoth, the position of her head changes completely between the first and the second shot. As the second shot ends, she begins to turn around, but in the next shot, she has already turned around. Also, Major Derlin's (the man dressed in grey) head has changed position. (00:23:05)
Revealing mistake: During the escape from Cloud City, watch as C-3PO's head strikes a lamp on the hull of the Millennium Falcon. It bends out of shape.
Continuity mistake: When the Empire ship shoots asteroids in the asteroid field, the first one explodes before the laser even hits it.
Continuity mistake: In the last part of the lightsaber duel, and in the following scenes, the color and seriousness of the wounds and bruises on Luke's face keep changing: For example, in the iconic segment where Luke reacts in shock and horror at Vader revealing himself to be his father, the injuries look quite nasty, but when he comes to a stop inside the tunnel after falling from the catwalk, they look far less severe. (01:49:30)