CONTEXT: Adolescent pregnancy, birth, abortion and sexually transmitted disease (STD) rates are much higher in the United States than in most other developed countries. METHODS: Government statistics or nationally representative survey data were supplemented with data collected by private organizations or for regional or local populations to conduct studies of adolescent births, abortions, sexual activity and contraceptive use in Canada, the United States, Sweden, France and Great Britain. RESULTS: Adolescent childbearing is more common in the United States (22% of women reported having had a child before age 20) than in Great Britain (15%), Canada (11%), France (6%) and Sweden (4%); differences are even greater for births to younger teenagers. A lower proportion of teenage pregnancies are resolved through abortion in the United States than in the other countries; however, because of their high pregnancy rate, U.S. teenagers have the highest abortion rate. The age of sexual debut varies little across countries, yet American teenagers are the most likely to have multiple partners. A greater proportion of U.S. women reported no contraceptive use at either first or recent intercourse (25% and 20%, respectively) than reported nonuse in France (11% and 12%, respectively), Great Britain (21% and 4%, respectively) and Sweden (22% and 7%, respectively). CONCLUSIONS: Data on contraceptive use are more important than data on sexual activity in explaining variation in levels of adolescent pregnancy and childbearing among the five developed countries; however, the higher level of multiple sexual partnership among American teenagers may help explain their higher STD rates.