Adolescent childbearing has adverse sequelae that are intensified when the onset of sexual activity takes place at a particularly early age. A relationship between the onset of sexual activity and the age of maturation has been demonstrated; as the mean age of menarche has become younger, a greater discontinuity has been created between physical development on the one hand and cognitive and emotional development on the other. Initiatives to prevent early sexual initiation and unintended pregnancy must be designed in that context and with an appreciation of normative social pressures. This report reviews research on adolescent development and sexual behavior, including the relationship between maturation and the onset of sexual activity, the timing of pregnancy risk, clinic utilization and reasons for delay in clinic attendance, and clusters of high-risk behaviors. It discusses the role of clinical interventions, suggesting ways in which those who treat adolescents can assist them in acquiring and maintaining protective behaviors.