Aggressive behavior committed by inpatients has significant negative effects on patients, clinical staff, the therapeutic milieu, and inpatient community as whole. Past research examining nonpsychiatric patient groups has suggested that elevated self-esteem and narcissism levels as well as self-serving theory of mind (ToM) biases may be robust predictors of aggressive behavior. In the present study, we examined whether these constructs were useful in predicting aggressive acts committed by psychiatric inpatients. Severity of psychiatric symptoms, demographic variables and patients' anger, and hostility severity were also examined. We found patients who committed acts of aggression were differentiated from their nonaggressive counterparts by exhibiting significantly higher levels of self-esteem and narcissistic superiority. In addition, aggressors demonstrated self-serving ToM biases, attributing more positive attributes to themselves, relative to their perceptions of how others viewed them. Aggressors also showed increased psychosis, fewer depressive symptoms, and had significantly fewer years of formal education than their nonaggressive peers. These results support and extend the view that in addition to clinical variables, specific personality traits and self-serving attributions are linked to aggressive behavior in acutely ill psychiatric patients.