State hospital psychiatric patients (100) consecutively admitted to a research ward who were screened to eliminate physical illness before admission were studied. An unusually high incidence of medical illness was found. Of these patients, 46% had an unrecognized medical illness that either cuased or exacerbated their psychiatric illness; 80% had physical illnesses requiring treatment; and 4% had precancerous conditions or illnesses. A workup consisting of psychiatric and physical examination, SMA-34 serum profile, urinalysis, ECG and EEG after sleep deprivation identified > 90% of medical illnesses present in this population. Such a battery should be part of the routine workup for all hospitalized psychiatric patients.