Leonard's mother, Dr. Beverly Hofstadter, is a psychiatrist and neuroscientist. She has a personality almost identical to Sheldon's, including strict speech patterns, lack of social conventions, and attention to detail, and she is principally responsible for Leonard's difficult childhood. Sheldon and Beverly have a friendly relationship where they share details of each other's lives. Leonard is upset with that fact that she tells Sheldon more than she tells him. After a night out of bonding and drinking with Penny, Beverly kisses Sheldon, but realizes there are no romantic feelings involved.
Leonard's father is briefly mentioned as an anthropologist. Sheldon reveals that Leonard's middle name, "Leakey", comes from famed archaeologist Louis Leakey, with whom Leonard's father had worked. Leonard is embarrassed by his middle name and its humorous connotations, and rarely mentions it, as the name is an obvious bum. Apparently his father was not very affectionate towards him either, when he mentions that he had to compete with the bones of an etruscan kid for his father's favor.
Though little is known about Leonard's extended family, a few references to it have been made. In the first episode, Sheldon and Leonard discuss Leonard's grandmother, who had visited them on Thanksgiving the year before. She has Alzheimer's disease and apparently "had an episode" during her visit, which resulted in her stripping off her clothes and carving the turkey. On Beverly's first visit, she tells Leonard that his uncle Floyd has died, which greatly upsets him (according to him, Floyd was the only family member he really liked). Leonard also has several other uncles, which Sheldon says are all very bald, and when they gather together, they look "like a half carton of eggs." Leonard describes his aunt, however, as being "one of the hairiest women you'll ever meet".