NEW YORK — Dr. Richard A. Isay, a psychiatrist, psychoanalyst, and gay-rights advocate who did not admit to himself that he was gay until he was 40, married, and a father, and who won a pitched battle to persuade his own profession to stop treating homosexuality as a disease, died on Thursday in Manhattan. He was 77.

The cause was cancer, said his son David. At his death, Richard Isay was a professor of psychiatry at Weill Cornell Medical College and a faculty member at the Columbia University Center for Psychoanalytic Training and Research.