COMT gene is a logical candidate gene for schizophrenia. Moreover, variations in the COMT Val158Met functional polymorphism have been associated with prefrontal cognitive abnormalities among patients with schizophrenia, healthy relatives and controls. In this study, using an epidemiologically-based sample of 130 patients experiencing a first-episode of a non-affective psychosis, we examined whether COMT Val158Met genotype influenced cognitive performance on the phenotypic expression of psychosis. We found no significant differences in any cognitive measure according to COMT genotype. These findings, together with previously published research, put the relationship between COMT genotype and cognitive performance in doubt.