The role of serum prolactin in sexual dysfunction has not yet been clarified. Moderate elevations of prolactin levels, without any associated disorder, occur frequently. A random group of 600 patients was studied to determine the level of prolactin in which medical treatment was necessary. Among these patients 23 (3.8%) presented hyperprolactinemia and were divided into two groups: Group 1--Twelve patients with prolactin levels ranging from 20 to 40 ng/ml, and Group 2--Eleven patients with levels higher than 40 ng/ml. In Group 1, prolactin of all patients returned to normal levels after treatment, but only one patient (8.3%) achieved full erection; on the other hand, in Group 2, nine out of eleven patients prolactin returned to normal after treatment and 77.7% achieved full erection.