Dallesandro's brother Bobby died in an autoerotic asphyxiation-related accident on December 31, 1977.
Dallesandro has been married three times. His first wife was named Leslie (the daughter of his father's girlfriend); they had a son, Michael, circa 1968. He has one other son, Joseph A Dallesandro Jr, born November 17, 1970 by his second wife Terry (Theresa), who divorced him in early 1978. He has since married again to Kim (Kimberly), and has a grandson by his son Joseph, a grandson and a granddaughter by his first son, Michael.
He currently manages a hotel in the heart of Hollywood, where he lives with his cat Booky. He has said: "I've lived such a full life. I've had such great things. There were some hardships, but overall everything has been great."