The hospital that Clerici's father is at is actually the Teatro Libera (Free Theater) at the Palazzo dei Congressi in EUR, a massive complex on the outskirts of Rome that was begun as a monument to the Fascist Government. This massive, modernist white marble complex and theater have appeared in several other films and television shows.
When Clerici asks the operator to connect him with Professor Quadri, the telephone number he gives is the (one-time) telephone number of Bernardo Bertolucci's idol Jean-Luc Godard. When Quadri answers the phone, Clerici recalls one of his lectures in which Quadri said "The time for reflection is over. Now is the time for action." This is the opening line in Godard's film The Little Soldier (1963).
Alberto Moravia's novel is told from an omniscient point of view. For the film adaptation, Bernardo Bertolucci chose to tell the story more from the viewpoint of the protagonist, whose memories and feelings are deliberately misleading and unreliable. Bertolucci's non-linear approach to the film's timeline only adds to the film's stream-of-consciousness feeling.
Bernardo Bertolucci was introduced by his then-girlfriend Maria Paola Maino to Alberto Moravia's novel. He was impressed by her description of the story, but because he locked in production on The Spider's Stratagem (1970), he had not actually read the novel when he pitched a film adaptation to Luigi Luraschi of Paramount Pictures, who agreed to fund and distribute the film. A month later, Bertolucci was reading the book with one hand, and writing the script with his typewriter in the other.
The film was in contention for the Golden Bear at the Berlin International Film Festival. However, a huge controversy over the inclusion of Michael Verhoeven's film O.K. (1970) resulted in the Festival being abandoned and no awards being given out.