Changes in the patient population at the Massachusetts Mental Health Center over a 20-year period were documented by examining the discharge records of the first six months for the years 1945, 1955, and 1965. Among those patients diagnosed as having affective disorders, there was a marked shift in the age distribution toward a younger population, predominantly female, with a marked increase in the proportion of depressive reactions and a decrease in manic-depressive and involutional psychotic diagnoses. The author suggests that these population changes may parallel the redefinition of mental illness and the greater acceptance of psychiatric hospitalization during the last 20 years.Abstract Teaser