OBJECTIVE: The study evaluated the Nurses' Observational Scale for Inpatient Evaluation (NOSIE), the Brief Psychiatric Rating Scale (BPRS), the Mini Mental State Examination (MMSE), and other measures as predictors of assaults that occurred during psychiatric hospitalization. METHODS: On admission, the MMSE was administered to 335 acutely ill psychiatric patients, and diagnostic and demographic data were recorded. Immediately after admission, patients were rated by nurses using the NOSIE and by psychologists using the BPRS. Patients who committed assaults during hospitalization (N = 47) and those who did not were compared, and relationships between several variables and assaults were evaluated by t tests, Mann-Whitney U tests, chi square tests, and analyses of variance. RESULTS: A high score on the irritability factor of the NOSIE and failure to complete the MMSE correctly predicted the occurrence or nonoccurrence of assault 81 percent of the time. None of the other variables examined were significantly related to assaults, including total scores on the BPRS and MMSE, psychiatric diagnosis, and several demographic variables. CONCLUSIONS: Scores on a test of distress level shortly after admission and failure to complete the MMSE on admission can help the clinician predict who will later engage in an assault.