Despite the lack of extrapyramidal side effects, some atypical antipsychotics can induce an increase in prolactinemia, as the conventional neuroleptics do. We decided to evaluate the effects of risperidone on serum prolactin levels and prolactin-related adverse effects in 20 outpatients of an Italian community psychiatric service. Patients enrolled in this study were on risperidone (2-8 mg per day; mean dose=4.15+/-0.4 mg per day) treatment in the period May-November 2002. The 20 patients, 13 women and 7 men (mean age=36.38+/-3.2 years for women and 29.7+/-2.2 for men) who accomplished inclusion criteria, participated in the study after giving informed written consent. Raised prolactin levels were observed in 13 (9 women and 4 men) out of 20 patients, but only 8 patients presented prolactin-related adverse effects, libido reduction being the most frequent. In this observational study, risperidone enhanced serum prolactin in 65% of patients. A good correlation was found between age and prolactin levels in pre-menopausal women, although no clear correlation among duration of treatment, dose used, prolactin levels and prolactin-related adverse effects could be established.