OBJECTIVE: The author's goal was to determine the frequency and distribution of neuropsychiatric diagnostic tests provided to general hospital patients with mental disorders. METHOD: Data from the 1989 National Hospital Discharge Survey were analyzed to determine the number, proportion, and general characteristics of 11,628 discharged patients with primary diagnoses of mental disorders who underwent computerized tomography (CT) scanning of the head, EEG, and magnetic resonance imaging (MRI) of the brain. RESULTS: Of the discharged patients with mental disorders, 5.1% had received CT scans, 2.8% had received EEGs, and 0.7% had received MRI. These rates were below the rates for patients discharged with primary diagnoses of neurological disorders but above the rates for patients discharged with primary diagnoses of other medical disorders. Among the patients discharged with mental disorder diagnoses, the likelihood of receiving a CT scan or an EEG was greater if the primary diagnosis was an organic disorder or if the secondary diagnosis was a medical disorder. Patients over age 65 were also more likely to have received a CT scan. Hospital size and location had a modest influence on the likelihood of receiving a CT scan or EEG, but the ownership of the hospital and the patient's source of payment were not significant influences. CONCLUSIONS: Neuropsychiatric diagnostic testing is selectively utilized in the routine treatment of general hospital psychiatric inpatients. Clinical variables rather than institutional or financial variables appear to be the most powerful predictors of which patients are selected to receive these tests.Abstract Teaser