Neurocognitive impairments are a core feature of schizophrenia (SCZ) and have been shown to impact patients' everyday lives, progress in psychosocial treatment, and functional outcome (e.g., Green, Kern, & Heaton, 2000). Although substance use disorders (SUDs) are a common comorbid diagnosis also associated with neurocognitive dysfunction, the literature on the neuropsychology of individuals with SCZ and SUDs is equivocal (Potvin, Stravo, & Pelletier, 2012; Tervo, 2007). The aim of the present study was to explore a possible additive effect of SUDs on neuropsychological impairment in SCZ using a novel research approach that emphasizes individual variability. In addition to SUDs, other clinical attributes and demographic characteristics that could account for the cognitive heterogeneity among individuals with SCZ were explored. Data were obtained from the Mental Illness and Neuroscience Discovery Clinical Imaging Consortium database. Participants included: patients with SCZ and a lifetime history of a SUD (SCZ+; n = 86), patients with SCZ without a SUD history (SCZ-; n = 69), and controls (n = 154). Widely used neuropsychological tasks were grouped into cognitive domains using a composite score approach with the control participants serving as a normative sample. Neuropsychological functioning of the patient sub-groups was compared using a MANOVA as well as Chi-square analyses of the frequency and extent of impairment within and across cognitive domains. Results yielded no significant differences between the patient subgroups. The current findings support the conclusion that regardless of statistical approach, within-group differences in neuropsychological functioning are larger than are between-group differences. Further results suggested that patients' age and cognitive reserve significantly predicted neuropsychological functioning over and above their history of SUDs. Implications of the findings for future research and clinical practice are discussed.