A sample of 528 successive admissions to the Phoenix Program, a voluntary inpatient treatment program for sex offenders, was studied in regards to serum prolactin levels. Serum prolactins were obtained as part of a battery of endocrine tests. A substantial number of patients had prolactin levels above the normal range, i.e., 21.0 microg/L. In this sample, fully 10.0% of the men showed elevated prolactin levels (the maximum being 41.0 microg/L), compared with an expected 2.5% according to laboratory norms. None of these individuals had clinical manifestations of prolactinoma. The significance of this increased rate of hyperprolactinemia in this sample of sexual offenders is unclear. There was a negative correlation with age and no correlation with other endocrine tests.