In recent years, a nationwide concern over the "epidemic" of teenage pregnancy has developed. Explanations for this phenomenon have ranged from poor sex education to promiscuity. This statement will review current data and information so that pediatricians responsible for the health care of adolescents can appreciate the implications and consequences of early childbearing. SEXUAL ACTIVITY AMONG ADOLESCENT GIRLS The term adolescence must be used with caution in describing the rapid biological, psychologic, and cognitive changes that take place during the teen years. Teenage girls are considerably different from each other in pubertal and emotional development. In making observations and interpretations about the attitudes, behaviors, and sexual activity of teenage girls, we must use developmental age rather than chronologic age as the standard for comparison. Sexual activity in 12-year-old girls living in intact households1,2 is unusual; therefore, the number of live infants born to mothers in this age group is small. However, more than 50% of 19-year-old girls have engaged in sexual activity, and their fertility rate is comparable to women in their 20s. The current problems with teenage pregnancies cannot be appreciated fully without understanding adolescent sexual behavior and the secular changes that have taken place. From 1900 to the early 1960s, sexual behavior in the unmarried, teenage population changed. A review of the earlier literature indicates that a significant increase (tenfold) in the incidence of sexual intercourse among single, teenage girls occurred in the early part of this century.3 Measureable changes in the attitude of adolescents toward sexuality became strikingly apparent in the 1960s.