Corrected entry: When Peter Pettigrew transforms himself into a rat and escapes, he leaves behind his clothes. In all Harry Potter films, including Prisoner of Azkaban, an Animagus is able to transform back and forth fully clothed.
Macalou
6th Aug 2004
Correction: This is not entirely correct. In Philosopher's Stone, Professor Magonagall turns from an unclothed cat into a woman. Same with Sirius Black in POA. Peter Pettigrew would only obtain his clothing upon changing into a man, not vice versa. Leaving his clothes behind wouldn't necessarily matter, as new clothes would, of course, magically reappear when he transforms back into human form.
Macalou