Co-writer and director Paul Mazursky was taking a cab to meet the casting director, and his cab driver talked so much, he thought she might be good in the movie. He had her park at the casting director's office and leave the meter running while she came inside and read for the part. She, Muriel Beerman, got the part as the taxi driver.
When Art Carney initially told Paul Mazursky that he loved the script, but felt that he was too young in his mid fifties to play Harry, Mazursky pointed out to Carney that he already had a natural bow-legged walk due to his World War II injuries, and could easily pass as an older man.
Art Carney won the Best Actor Oscar for this film, beating out some heavyweight competition: Albert Finney in Le crime de l'Orient-Express (1974), Dustin Hoffman in Lenny (1974), Jack Nicholson in Chinatown (1974), and Al Pacino in Le Parrain, 2ᵉ partie (1974).
James Cagney was originally offered the role of Harry. Other people considered for the role were Sir Laurence Olivier and Cary Grant before Art Carney was finally cast. Paul Mazursky's words to Carney were, "You'll win an Oscar", which turned out to be prophetic.
Pieces of liver were placed around Art Carney in order to attract the cats that played Tonto into cuddling with Carney in pivotal scenes.