A study of 658 consecutive psychiatric outpatients receiving careful medical and biochemical evaluation, defined an incidence of medical disorders productive of psychiatric symptoms in 9.1% of cases. The most frequent presentations were of depression, confusion, anxiety, and speech or memory disorders. The presence of visual hallucinations was believed to indicate medical etiology until proved otherwise. Major illnesses presenting with psychiatric symptoms in order of frequency were infectious, pulmonary, thyroid, diabetic, hematopoietic, hepatic and CNS diseases. Forty-six percent of these patients suffered from medical illnesses previously unknown to either them or their physician. A plea is made for careful medical evaluation of psychiatric patients.