Irregular discharges, previously studied on psychiatric or substance abuse treatment units, are a particular problem for dual diagnosis units. We examined demographic and clinical variables for their association with irregular discharge from an acute dual diagnosis inpatient unit, retrospectively reviewing 316 consecutive admissions. One hundred and nineteen patients (37.7%) were irregularly discharged (61 AMA, 31 administrative, 27 elopements), staying an average of 18.8 days compared with 51.4 days for those regularly discharged(p<. 001). Younger age(p=. 007) and discharge diagnosis of antisocial personality disorder(p<. 001) were associated with irregular discharge; the attending psychiatrist was also significant(p=. 016). Demographic variables (sex, ethnicity, marital status, religion, employment, education, living circumstances), Axis I diagnosis, and type and number of substances abused were not predictive of discharge type. Patients irregularly discharged within the first week (40% of irregular discharges) were significantly less likely to have known legal involvement (p =. 006). No significant temporal clustering of irregular discharges was found on a daily, weekly, or monthly basis, nor was a seasonal pattern detected. These findings are generally consistent with several pre-DSM-III studies on nondual diagnosis units, but more specifically highlight the diagnosis of antisocial personality. Regarding program completion, they suggest that risk factors for irregular discharge (substance abuse, antisocial personality, characteristics of the doctor-patient relationship, problems of younger patients) have not been adequately addressed simply by creating dual diagnosis units. Further programming study appears warranted to address the problem of patient retention on dual diagnosis units.