The department was founded in 1926 as part of a restructuring of the New York state government, and was given responsibility for people diagnosed with mental retardation, mental illness or epilepsy. Dr. Frederick W. Parsons was appointed the first department Commissioner in January, 1927. He was replaced by Dr. William J. Tiffany in 1937, who then resigned in 1943 over an investigation into handling of an outbreak of amoebic dysentery at Creedmoor State Hospital. By 1950, the department had grown into the largest agency of the New York state government, with more than 24,000 employees and an operating cost exceeding a third of the state budget.
The Office of Alcoholism and Substance Abuse was transferred from the New York State Department of Health to the Department of Mental Hygiene in 1962. In 1978, the Department of Mental Hygiene was reorganized into the autonomous Office of Alcoholism and Substance Abuse, Office of Mental Health (OMH), and the Office of Mental Retardation and Developmental Disabilities (OMRDD). These three offices are headed up by a Commissioner who also serves on a council that performs inter-office coordination. The OMRDD is now the Office for People With Developmental Disabilities (OPWDD). The Office of Alcoholism and Substance Abuse is now the Office of Alcoholism and Substance Abuse Services (OASAS).
^Mental Hygiene Law § 5.01. "There shall continue to be in the state government a department of mental hygiene. Within the department there shall be the following autonomous offices: (1) office of mental health; (2) office for people with developmental disabilities; (3) office of alcoholism and substance abuse."