The primary goals of compulsory, inpatient, psychiatric treatment are to decrease dangerous behaviors and help improve functioning so that a safe discharge to a less restrictive environment can be obtained. This study examined the aggression rates, levels of functioning, and treatment adherence for persons treated for schizophrenia (N = 506) compared with persons treated for borderline personality disorder (BPD) (N = 98) in an inpatient psychiatric facility. Over half of persons engaged in at least one incident of aggressive behavior during hospitalization. Differences in the types of aggression and functional deficits between these two clinical sub-groups were found. In addition, overall impairment increased the likelihood of aggressive behavior for persons diagnosed with schizophrenia, whereas irritability and social dependence increased the risk of aggression for persons diagnosed with BPD. Treatment interventions that target the improvement of these deficits may help reduce the intensity and severity of aggressive behaviors and help improve functioning and discharge readiness.