Accurately predicting inpatient aggression is an important endeavor. The current study investigated inpatient aggression over a six-month time period in a sample of 152 male forensic patients. We assessed constructs of psychopathy, anger, and active symptoms of mental illness and tested their ability to predict reactive and instrumental aggression. Across all levels of analyses, anger and active symptoms of mental illness predicted reactive aggression. Traits of psychopathy, which demonstrated no relationship to reactive aggression, were a robust predictor of instrumental aggression. This study (a) reestablishes psychopathy as a clinically useful construct in predicting inpatient instrumental aggression, (b) provides some validation for the reactive/instrumental aggression paradigm in forensic inpatients, and (c) makes recommendations for integrating risk assessment results into treatment interventions.