Abstract This study evaluated the psychiatric symptoms, psychosocial problems, and treatment response of personality-disordered substance abusers receiving services within a homeless drop-in center. Fifty-two homeless clients were assessed after program admission and randomly assigned to receive either individual psychotherapy focused on personality disorder and substance abuse relapse prevention (dual-focus schema therapy [DFST]) or standard group substance abuse counseling (SAC). Client functioning was assessed using measures of personality disorder, psychiatric symptoms, early maladaptive schemas, interpersonal problems, and addiction-related psychosocial impairment. Therapy retention (total weeks in treatment) and utilization (number of weeks in which sessions were attended) were the primary outcomes. Although rates of cluster B personality disorders were comparable to other substance dependent samples, clusters A and C disorders were disproportionately more common. Clients reported significant psychiatric symptoms, criminality, and psychosocial impairment, yet made limited lifetime use of mental health services. Overall, there was greater utilization of individual DFST than group SAC. However, clients with more severe personality disorder symptoms demonstrated better utilization of SAC than DFST.