Identifying the characteristics of men who drop out of batterers' programs is crucial for prevention, intervention, and research. This article reviews studies of program attrition to establish a description of men who fail to complete group-based batterers' interventions. Studies indicate that men who drop out are more likely to be unemployed, be unmarried and/or childless, have lower incomes, and less education than men who remain. Dropouts are also more likely to have a criminal history, to report substance abuse or related problems, and to present with particular relationship concerns or orientations. The relationship between court referral and dropout was inconsistent across studies and may vary according to socioeconomic status. Psychopathology is consistently related to dropout, but may be associated with other factors (e.g., comorbidity or referral source). Age, race, childhood exposure to violence, and battering history are all inconsistently associated with dropping out. The implications of these findings for research and program development are discussed.