Objective: This study examines the relationship between neuropsychological test performance and antipsychotic medication type/dosage. Given the growing body of evidence implicating the dopaminergic system in cognitive and motivational deficits in schizophrenia, the potential neurocognitive effects of long-term antipsychotic usage are of particular concern. Method: 280 individuals with a serious mental illness (SMI) diagnosis were recruited from a community mental health center and were administered a battery of neuropsychological tests: Neuropsychological Assessment Battery Screener (S-NAB), Trail Making Test (TMT), Controlled Oral Word Association Test (COWAT), and WAIS-III Letter-Number Sequencing (LNS). Data on concurrently prescribed medications were available for 111 of these individuals. Bivariate correlations were utilized to examine the relationships among medication type/dosage and performance. Results: Dosage was negatively associated with performance on WAIS-III LNS (aripiprazole, r = −.46, p < .01; olanzapine, r = −.54, p < .01), S-NAB Digits Forward (aripiprazole, r = −.32, p = .05; olanzapine, r = −.35, p = .05), S-NAB Digits Backward (olanzapine, r = −.48, p < .01), S-NAB Auditory Comprehension (aripiprazole, r = −.42, p < .01; olanzapine, r = −.41, p < .05), S-NAB Story Learning Immediate Recall (aripiprazole, r = −.40, p < .05), and S-NAB Story Learning Delayed Recall (aripiprazole, r = −.40, p < .05; olanzapine, r = −.37, p < .05). Higher dosages of quetiapine, clozapine, risperidone, ziprasidone, and haloperidol were not associated with decreased performance on any test. Conclusion: Negative dose effects were isolated to individuals prescribed olanzapine and aripiprazole. Findings provide further evidence of the relationship between specific antipsychotic medications and performance on neuropsychological tests. They also highlight the need to determine minimal effective dosages for aripiprazole and olanzapine given the evidence that higher doses of these medications may affect attention and other neurocognitive domains.