At the beginning of the pilot, Sondra, the Huxtables' eldest daughter, was added as an afterthought. However, when Clair Huxtable mentions the couple's four children, they decide to add another child to represent the results of a good upbringing. The casting came down to 26-year-old Sabrina Le Beauf and 21-year-old Whitney Houston. LeBeauf was too old for the role, only ten years younger than Phylicia Rashad. However, Houston refused to sign a contract committing her to the show as she wanted to pursue her singing career. This forced the producer's hand, and LeBeauf was given the role of Sondra.
Peter Costa, who played Huxtable neighbor and Rudy's playmate Peter, suffered from stage fright and often forgot his lines. As a result, his character's communication via trademark facial expressions and always running out of the house at the first sign of trouble.
Cliff was originally going to be a chauffeur. Bill Cosby's wife, Camille, suggested making him a doctor, more fitting with the show's agenda to shatter racial stereotyping.
Rudy was originally going to be a son. When a suitable boy could not be found, girls could audition.