Relatively uncommon, nonfamilial sexual abuse usually involves an adult male perpetrator and appears to occur as a result of abnormal sexual preferences or in situations where normal sexual preferences are thwarted. Juvenile sexual offenders may show signs of immature psychosexual development or may reflect an early manifestation of pedophilia or aggressive sexual behavior. Incest is the most common form of sexual abuse. The dynamics of mother-son, father-daughter, and sibling (sister-sister, brother-brother, and sister-brother) incest varies. Most attention has focused on father-daughter incest. Research suggests a strong role of intrafamilial dynamics in which needs, relationships, and personality characteristics of the mother, father, and daughter interact. Mother-son incest may be initiated by either party and is often indicative of serious emotional disturbance. Father-son incest while rare, is the most common form of homosexual incest and may be related to the parent's unresolved adolescent sexual conflicts. Sibling incest, depending on the age of the participants, its duration, and intent, may be regarded as developmentally appropriate or not. In most cases, sibling incest is less enduring than parent-child incest. Child pornography appears to attract participants either through offers of monetary or other rewards or is an attempt by parents or others to memorialize their sexual relationship with a child. Child prostitution usually involves some form of payment, frequently to runaways trying to survive. While the causes of sexual abuse are varied, it is clear that social, emotional, psychological, and developmental factors all contribute. It may be the result of learned behavior, earlier deprivation of nurturing, or questioning or exploration of sexual identity. Included are 10 references.