Family and background

George is half Italian (on his father's side) and presumably Jewish (on his mother's), the son of Frank and Estelle Costanza, who are described as "psychopath[s]" by Jerry ("The Puffy Shirt"); "loud" and "always fighting" by Helen Seinfeld ("The Raincoats, Part 1"); and "sick" by the father of Susan Ross ("The Rye"). The constant bickering and bizarre behavior of his parents is often cited as a reason for George's adult neurosis and eccentricity: Jerry comments that George "could have been normal" had the Costanzas divorced thirty years earlier ("The Chinese Woman"), and George describes himself as "the result of my parents having stayed together" ("The Shoes"). Nevertheless, George can be fiercely defensive on his parents' behalf if they are snubbed by others, as when Jerry's own parents avoided dinner with them in "The Raincoats, Part 1".

In "The Suicide", George makes reference to a brother who "once impregnated a woman named Pauline". The brother is referenced again in "The Parking Space" when George explains that no one in his family pays for parking, but the brother is never referenced elsewhere, nor does he make an appearance in the series.

George has two known cousins. One of them is Shelly, who appeared in "The Contest", and his other cousin Rhisa appears in "The Junk Mail", referred to by George as Frank's "brother's daughter", although this uncle does not appear, either; however, it is mentioned at another time that George has an uncle Moe, who "died a young man" ("The Money"). George also had an aunt, "Aunt Baby", who died at the age of 7 of internal problems ("The Money"). When asked by his wife how old Aunt Baby would be today if she had lived, Frank Costanza replied, "she never woulda made it". In "The Doll", it is revealed that Frank Costanza has a cousin, Carlo, in Tuscany. The townspeople in Tuscany refer to Carlo as the "village idiot". As of the first season episode "The Robbery" George had a living grandmother and grandfather whom he had recently visited. These are likely his father's parents as in another episode George asks his mother about her mother, whom he never really knew and had only seen pictures of.

• George attended John F. Kennedy High School and Queens College with Jerry. They played basketball together in high school.
• George's favorite drink is Bosco mixed with milk, as referenced in "The Secret Code".
• George gets out of relationships by telling the girl, "It's not you, it's me." In "The Lip Reader", a girl tries to use it on him, and he tells her that he invented it.
• George, like Jerry, is a fan of the New York Mets, the New York Knicks, and the New York Rangers. Later George becomes a fan of the New York Yankees when he begins working for the team.