Thomas Szasz, a psychiatrist whose 1961 book “The Myth of Mental Illness” questioned the legitimacy of his field and provided the intellectual grounding for generations of critics, patient advocates and antipsychiatry activists, making enemies of many fellow doctors, died Saturday at his home in Manlius, N.Y. He was 92.

He died after a fall, his daughter Dr. Margot Szasz Peters said.

Dr. Szasz (pronounced sahz) published his critique at a particularly vulnerable moment for psychiatry. With Freudian theorizing just beginning to fall out of favor, the field was trying to become more medically oriented and empirically based. Fresh from Freudian training himself, Dr. Szasz saw psychiatry’s medical foundation as shaky at best, and his book hammered away, placing the discipline “in the company of alchemy and astrology.”

The book became a sensation in mental health circles, as well as a bible for those who felt misused by the mental health system....