Use of the Aberrant Behavior Checklist (ABC) as a tool for measuring the effectiveness of psychopharmacological and other therapeutic interventions for problem behaviors in autism has increased in recent years. With a sample (n = 236) of staff-rated individuals with low-functioning autism spectrum disorders (ASDs), the present exploratory factor analysis (EFA) supported a seven-factor solution that expands upon the measure's published structure. Four factors were similar to those in the published solution; in addition, the published Lethargy / Social Withdrawal factor was replaced by one factor measuring Social Withdrawal and one measuring Lethargy; and a Self-injurious Behavior factor emerged as well. Internal consistency of the retained factors was high. Using subsets of the above sample, comparisons of the retained factors' score composites to instruments hypothesized to measure similar constructs (convergent validity) and dissimilar constructs (divergent validity) provided initial evidence of concurrent validity. This study expands on previous ABC factor analytic work in part by (1) its consideration of multiple factor solutions, (2) providing a solution not found in previous ABC literature, and (3) attempting to improve on some methodological concerns in the one previous factor analysis of the ABC with an ASD sample. Although this study provides necessary psychometric support for the use of the ABC with the ASD population, future research should attempt to validate the present factor structure, extend the scope and depth of concurrent validity tests, and measure other psychometric properties of the ABC when used with this population.