There is a scene near the beginning where a swarm of soot sprites (susuwatari) comes boiling out of a crack in the wall, suddenly; when that happened, my girlfriend jumped and yelped.
I suppose I should have told her beforehand that Totoro is a kids' movie and that nothing bad happens. She might have been less apprehensive. Miyazaki did play up the "scary" a bit during that part of the movie.
But when all was said and done she told me she'd really enjoyed the movie, so it's all good, I guess.