Studies have found higher rates of mental illnesses in jails and prisons than in the community, as well as increasing evidence of the relationship between mental illness and aggression among mentally ill offenders. Because of this potential risk for violence among inmates, especially among mentally ill inmates, identification of a reliable and valid screening measure of violence potential is crucial for treatment planning and inmate management. One screening instrument that has shown to be effective in measuring anger and aggression is the Buss-Perry Aggression Questionnaire (BPAQ). This study examined the factor structure of the BPAQ with a sample of male offenders in a State correctional psychiatric hospital and driven by 3 research questions: (1) which of 6 previous factor models of the BPAQ would fit the data from male inmates; (2) would the data support a 1-factor, 2-factor, or 4-factor model of aggression; and (3) would the refined 12-item BPAQ exhibit adequate measurement characteristics for applied use with a male prison population? The refined 4-factor, 12-item model provided the best fit for the data. Confidence in the results was bolstered by the use of confirmatory, rather than exploratory, factor analyses and that the results cross-validated with an independent sample. Tables, references