Walter Matthau was the first choice for the Eli Wallach part but was asking $200,000, so the producers opted for the less expensive George C. Scott. Scott had been on the set for a few weeks before shooting began. However, on his first day of shooting, he didn't show up until after lunch, and director William Wyler decided to fire him. He was already finding it difficult to handle two heavy drinkers, Peter O'Toole and Hugh Griffith, and the prospect of a third was just too overwhelming. On hearing of Scott's removal from the production, Audrey Hepburn became quite inconsolable.
After Nicole dresses up as a cleaning lady, Simon Dermott says, "That does it. For one thing, it gives Givenchy a night off." Hubert de Givenchy was Audrey Hepburn's costume designer.
During production, Hugh Griffith was fired for persistent eccentric behavior, including walking around naked through the corridors of the George V Hotel holding a "Do not disturb" sign over his pubic area, which he'd altered to read "Do disturb".
In the original source short story, the statue is life-sized.
During a night shoot, director William Wyler asked Peter O'Toole to take Audrey Hepburn, who was dressed in only a thin nightgown and jacket, to his trailer so she could get warmed up. O'Toole gave her some brandy to help with the warming up, and by the time she was needed on set, Hepburn, being less used to alcohol than O'Toole, was tipsy and knocked over the lights when she had to drive the car.