Michael McKean and David L. Lander were originally hired as writers/consultants. They wrote themselves into the show as Lenny and Squiggy, two characters they created in college. Squiggy was originally named "Ant'ny" but the producers wanted the two boys' names to coincide with the girls'. Squiggy was the name of an unseen character in McKean and Lander's "Lenny and Ant'ny" sketches.
According to the book Live from New York: An Uncensored History of Saturday Night Live, Penny Marshall stated that Gilda Radner was considered for the part of Shirley.
Various Happy Days cast members have talked about the vicious fights next door on set of Laverne and Shirley, so loud that they would listen with glasses to the wall.
After The Odd Couple (1970) ceased production, the apartment set on that show was modified to become Laverne and Shirley's apartment.
With the death of Cindy Williams on January 25, 2023, Michael McKean is the only surviving member of the regular cast.