The program, called the Program for the Aggressive Mentally Ill Offender (PAMIO), was begun in 1990 by the Texas Department of Criminal Justice. The program has beds for 458 violent male offenders. The purpose of PAMIO treatment is to decrease an offender's propensity for hostile aggression while increasing his ability to meet his needs by the use of prosocial behaviors. Treatment is multimodal and consists of biological and psychosocial interventions such as extensive biopsychosocial assessment, psychotropic medication (when necessary), individual and group therapies, and habilitation therapies (occupation therapy, music therapy, and recreational therapy). The program uses behavioral and cognitive-behavioral therapeutic techniques such as extinction responding, a level system, and cognitive restructuring. The typical offender enrolled in PAMIO receives treatment for approximately 18 months; after program completion, the graduate can receive follow-up treatment in general population units. Paired t tests showed that after PAMIO treatment, there was a significant decrease in the annual rates of total disciplinary actions, staff assaults, inmate assaults, and good time lost. This improvement appeared to be directly related to treatment effects. 1 table and 18 references