This study compared psychiatric outpatients who were never, former, and current substance abusers on psychiatric, social, and cognitive functioning. Fifty-six outpatients with schizophrenia-spectrum and bipolar disorders volunteered to complete diagnostic and social role function interviews, selfreport inventories, and neuropsychological tests. Multinomial logit regression analyses indicated that current and former abusers reported greater subjective feelings of distress than those who never abused. Contrary to expectations, however, both groups of substance abusers performed better on non-verbal cognitive tests compared to those who never abused. Differences in social functioning were also observed: former abusers demonstrated better instrumental role functioning than those who never abused. This pattern of findings challenges assumptions about additive effects of comorbid disorders on cognitive and social functioning. Keywords schizophrenia; substance abuse; psychiatric distress; cognitive function; social function Persons living with a severe and persistent mental illness (SPMI; e.g., schizophrenia, bipolar disorder) often abuse alcohol or other drugs. At least 20% of all persons diagnosed with a SPMI have a current substance use disorder (SUD), and approximately 50% meet criteria for a SUD during their life (Regier et al., 1990). This comorbidity warrants greater attention because both classes of disorders are associated with pervasive impairment.Persons living with a SPMI routinely experience impairment in cognitive and social domains. For example, schizophrenia is often associated with a generalized pattern of cognitive deficits, including impairments in attention, memory, abstract thinking, problem solving, and tasks involving effortful processing (e.g., Braff, 1993;Saykin et al., 1991). Such impairment predates experience with neuroleptic or other treatments; however, considerable variability exists among patients with schizophrenia on neuropsychological tests (Mohamed, Paulsen, O'Leary, Arndt, & Andreasen, 1999;Saykin et al., 1994). Similarly, bipolar patients also demonstrate deficits in attention, learning and memory, especially during manic phases of the illness (Martinez-Aran et al., 2000;Murphy & Sahakian, 2001). Social/occupational dysfunction is a necessary criterion for diagnosis of both schizophrenia and bipolar disorder (Diagnostic and Statistical Manual of Mental Disorders [DSM-IV], American Psychiatric Association [APA], 1994), and often includes impaired ability to perform expected role functions in the community. In particular, persons with schizophrenia experience stable and pervasive social skill deficits (e.g., Mueser, Bellack, Douglas, & Morrison, 1991 (Green, 1996;Liddle, 2000).Substance use disorders also engender cognitive, social, and psychiatric problems. Prolonged abuse of alcohol is associated with impairment in abstraction, problem solving, memory, and perceptual-motor tasks (Chelune & Parker, 1981;Evert & Oscar-Berman, 1995). Polydrug abuse, especially the use of opiat...