Information was presented on the psychometric characteristics of the Aberrant Behavior Checklist. The internal consistency and test-retest reliability of the Checklist appeared to be very good. Interrater reliability tended to vary across raters and subscales and ranged from mediocre to good but was generally in the moderate range and acceptable for research purposes. Validity was assessed by comparing Checklist scores for residents presenting with attributes thought to reflect varying degrees of social adaptation. Validity was also evaluated by comparing Aberrant Behavior Checklist scores with ratings on adaptive behavior scales and with objective observations of behavior. In general, validity was established for most Aberrant Behavior Checklist subscales. Preliminary data from drug investigations suggested that the Checklist may provide a useful adjunct for the assessment of psychotropic drug effects.