Until recently, discussions of sexual abuse of children have focused mainly on females. The definition of sexual abuse of boys has been hampered by common presumptions that boys often initiate the sexual encounters and that they are less negatively affected than girls by these encounters. Nevertheless, sexual encounters between prepubertal males and adults should be defined as the sexual abuse of boys. Data from four surveys show consistently that from 2.5 to 5 percent of boys are sexually victimized before age 13. Comparison with similar studies of girls indicates that two to three girls are victimized for every boy. Boys are more likely than girls to be victimized by someone outside the family, perhaps because of the characteristics of sex offenders. The abuse of boys is more likely to be reported to the police than to a hospital or child protective agency. Data tables, notes, and a list of 33 references are supplied.