Curse of Frankenstein, 1957, scared the crap out of me when I was ten. Of course it would do the same to any ten year old, if the movie is ever shown, being as old as it is.
It didn't have Boris as the monster but Christopher Lee played "sweetie" and Peter Cushing played the doc. But I have to say that Lee was much more scarier than Boris Karloff. The American film company that created Boris's monster wouldn't let British Hammer use the monster's makeup. So Hammer came up with their own, and it was more effective, because it was more realistic, than a bucket headed Karloff.