To determine factors in the sexual abuse of boys, we reviewed medical records of 140 boys who were seen for evaluation at the Children's Hospital and Health Center in San Diego from 1979 to March 1984. Many of the boys were seen by one of the authors. Boys represented 9% of the 1,748 sexual abuse victims. The incidence in males increasd from 7% in 1979 to 1980 to 11% in 1983. The boys were from 1 to 17 years of age. The majority of boys gave a clear, consistent, and credible history of sexual abuse. Eighty-five percent of the boys were abused by a relative or acquaintance. Physical evidence of sexual abuse was present in 95 (68%) of the victims. This paper emphasizes that boys, too, are at considerable risk for sexual abuse and that subtle physical findings of molestation are common when the child is examined by a trained, experienced physician.