Continuity mistake: When Dr. Seward first goes to see Renfield, he gets bitten on the right side of his neck, but then grabs the left side as if in pain.
Continuity mistake: At Lucy's dinner party, we see Jack Seward pick his hat up off the sofa so Quincy Morris does not sit on it. Once Quincy sits down, he gets a funny look on his face and then magically pulls Seward's crumpled hat out from under his butt.
Factual error: When Mina is with Dracula within Dr. Seward's room, she is wearing a white nightgown through which, at times, you can see her tiny underwear (more visible when he confesses to be Dracula and she is upset about him having killed Lucy - turning her into a vampire), in a fashion that would not be likely to be worn by women in the late 19th century.
Revealing mistake: When they are in the crypt to kill Lucy, they open the stone lid and look down. Clearly you can see glass on top of the inner coffin, yet later when Lucy goes in the coffin there is no glass.
Continuity mistake: When the wolf scares Mina in the movie theatre, her hat switches back and forth from being forward on her head, to being tilted back. It does this in about 5 shots.
Audio problem: When Dracula and Mina first meet on the street they begin to speak. Dracula's voice has not been dubbed during the first sentence or two. Then in mid stream his voice changes from a high pitched regular rehearsal voice to the heavily accented Romanian voice used throughout the rest of the picture.