Cass's parents have never been seen. His father, still unnamed, died of heart failure when Cass was a teenager.

Cass has not had contact with his mother, Claudia Winthrop, for about 20 years. The rift between them is due to something that happened when Cass was still living at home. He had a relationship with one of his mother's friends, but he never slept with her. This woman became pregnant, and told everyone that Cass was the father. Though he maintained that he couldn't be the father, Claudia refused to believe him. She henceforth cut him out of her life completely, and the two haven't spoken since.

Cass has a daughter named Charlotte "Charlie" Frame Winthrop, born in February of 1994. Charlie was born with a heart defect. She had surgery two months after her birth, and she has been all right since then.

Cass also conceived two children that miscarried, once in 1991 and in 1995.

Cass had an older brother (name unknown) who died aged two months from the same defect that his daughter now suffers from.

Stacey Winthrop. Stacey is a lawyer just like Cass, and they have often worked as partners. She is currently living in Los Angeles. Cass and Stacey are close.

Morgan Winthrop. The existence of Cass's brother was mentioned as early as 1988. When Morgan came to Bay City in 1993, it was the first time Cass had seen him in 15 years. In 1994, Cass and Morgan were at odds due to Cass's paranoid belief that Morgan was having an affair with Cass's wife Frankie Frame. But as this misconception was due to Cass's illness it was shortly cleared up.

In late 1995, Cass and Morgan had a major falling out over Cass's decision to act as Laurie Michaels' lawyer in her lawsuit against the hospital. Cass was forced to attack Morgan and his friend Courtney Evans, and Morgan could not forgive Cass for what he considered to be betrayal. They made up by mid-1996.

Other Relatives
Megan Singleton (RIP), niece (Stacey's daughter was killed in a car crash in 1987 while on a camping trip with her father. The driver was never apprehended). Alan Winthrop, "rich" cousin (1983).