Treatment with risperidone is associated with prolactin (PRL) elevation, and PRL elevations are associated with erectile dysfunction (ED). We evaluated whether the PRL elevations caused by risperidone treatment of subjects with schizophrenia are associated with objective measures of erectile function. Subjects were hospitalized for 2 nights, and serum measurements of PRL, total testosterone, and free and weakly bound testosterone were performed in the morning and afternoon of each day. Risperidone levels, parent compound, and 9-hydroxy metabolite levels were drawn on the first day. Erectile function assessments, using the RigiScan, an instrument that measures nocturnal penile tumescence and rigidity, were performed on both nights. Consistent with previous reports, the correlation between total risperidone level and PRL was very high (r = 0.92, df = 12, P < 0.0001), but risperidone did not appear to affect either testosterone (r = 0.29, df = 5, P = 0.51) or free and weakly bound testosterone (r = -0.11, df = 10, P = 0.72). Contrary to expectations, PRL levels from the second night were positively correlated with erectile function (r = 0.68, df = 9, P = 0.022). Using objective measures, we were unable to confirm a detrimental association between PRL levels and male erectile function. These results are tentative given the small sample.