"Cool" was such a demanding number for the performers, Harvey Evans (aka Harvey Hohnecker), who played Mouthpiece, later stated that the actors ritually burned their kneepads upon wrapping the scene.
"West Side Story" played for almost two years on stage in New York, racking up a total of 732 performances.
Audrey Hepburn was offered the role of Maria, but she turned it down, because she was pregnant with Sean H. Ferrer at the time.
Robert Wise wanted the film to have a single rising line of tension, with no light moments after the rumble. Therefore, "I Feel Pretty" was moved earlier, and the positions of "Cool" and "Gee, Officer Krupke" were reversed. Those who feel that the sassy, light-hearted tone of "Gee, Officer Krupke" is out of place following the deaths that end the first act prefer the film's ordering of the numbers. The placement of "I Feel Pretty" and "Gee, Officer Krumpke" after the Rumble in the stage version was meant to help cheer people up after the deaths of Bernardo and Riff, as audiences were not used to death occurring in Broadway musicals. This issue is still heatedly debated among the film's fans.
Jerome Robbins completed four numbers - the Prologue, "Cool", "I Feel Pretty" and "America" - before he was removed from the project.
Jerome Robbins initially refused to work on the film unless he could direct it. Producer Walter Mirisch was nervous about handing the reins entirely over to Robbins, who had never made a film before, so he enlisted Robert Wise to direct the drama while Robbins would handle the singing and dancing sequences. Robbins developed a habit of shooting numerous takes of each scene, to the point where the film went over budget and behind schedule. This led to his firing.
Jerome Robbins rehearsed with the dancers for three months before shooting began. Once location shooting began, however, he kept revising and revising his original choreography. The dancers all claimed that they had never worked so hard on a dance piece, and most of them at one point or another sustained injuries during shooting.
Jerome Robbins' propensity for filming and re-filming scenes in his quest for perfection led to the movie going over budget and falling behind schedule. Robbins was fired by Mirisch Pictures, the production company, when shooting was about 60% finished, and director Robert Wise completed the filming alone (the original arrangement had been for Robbins to direct all of the song-and-dance sequences and Wise to direct everything else).
Marni Nixon (who dubbed for Natalie Wood) had to do the end of quintet for Rita Moreno. The reason was that Betty Wand and Moreno both had colds and could not sing, so the filmmakers asked Nixon to do the end. So she is singing two voices at once.
Eliot Feld (Baby John) collapsed and ended up hospitalized with pneumonia during the demanding filming of "Cool".
Chita Rivera originated the role of Anita when West Side Story premiered at New York's Winter Garden Theatre (September 26, 1957). Rita Moreno later played Anita in the film adaptation of the show.
Gus Trikonis who played Indio, one of the Puerto Rican Sharks - and who is actually Greek - is the brother of Gina Trikonis, who played Graziella, the tough red-haired Italian girlfriend of Riff, leader of the Jets.
Russ Tamblyn (Riff) was dubbed for "The Jet Song" by Tucker Smith, who played Ice, his lieutenant in the movie.
Russ Tamblyn had originally tried out for the role of Tony. It was down to just him and Richard Beymer, and Beymer ended up getting it. But then the casting directors called him back and asked him to read for Riff, and he got the part.
Rita Moreno's singing voice was dubbed by Betty Wand only for "A Boy Like That" since it was below her range. Moreno sang "America" and "Quintet" herself.
George Chakiris (Bernardo) had previously played "Riff" in the London production. Tony Mordente (Action) had played "A-rab."
Betty Wand sued to get a percentage of the movie-album sales, having dubbed part of Rita Moreno's singing. The dispute was settled out-of-court.