Adrien Brody lost 14 kg (31 lb) for the role of Wladyslaw Szpilman by eating a daily diet of two boiled eggs and green tea for breakfast, a little chicken for lunch, and a small piece of fish or chicken with steamed vegetables for dinner over a six week period. Initially his weight was 73 kg (161 lb).
Roman Polanski himself experienced the Holocaust. His parents were sent to two different concentration camps: his father to Mauthausen-Gusen in Austria, where he survived the war, and his mother to Auschwitz where she was murdered.
The music played for the German officer in the film was actually an edit of Frédéric Chopin's Ballade No.1 in G Minor, (Op. 23, No. 1). In real life, Wladyslaw Szpilman played Chopin's Nocturne No.1 in C# Minor.
The film is based on the memoirs of Wladyslaw Szpilman. The director Roman Polanski tried to make the film as faithful of an adaptation as possible, with additional inspiration coming from events that happened to him while he was a boy during the war.
The trivia items below may give away important plot points.
A nuance for those who don't speak German: In general, the German officers use the informal version of "you" ("du," etc.) when talking to the Jews, which reflects their views (you wouldn't talk to adult strangers that way); however, Hosenfeld (the officer who discovers Wladyslaw Szpilman in hiding) always uses the proper formal form ("Sie," etc.) because of the way he personally feels.