Some renal transplant patients show cognitive, emotional, and behavioral changes as part of possible neurotoxic effects associated with immunosuppressive medication, especially tacrolimus. This study evaluated effects of immunosuppressive drugs on some cognitive tasks. Patients treated with sirolimus and cyclosporine reported some of the noncognitive side effects related to immunosuppressive treatment. We observed attention and working memory impairment in patients treated with sirolimus or tacrolimus. Performance of cyclosporine-treated subjects was similar to that of healthy volunteer controls. Since the mood, anxiety, and sleep patterns measured were unaffected, it could be concluded that the cognitive deficit found was partly related to treatment.