During the 1970s, there was a decline in adolescent childbearing in the United States and, among teenagers who were sexually active, there was a decline in pregnancy rates as well. To what extent was increased enrollment by teenagers in federally funded family planning clinics responsible for these declines? Areal multivariate analysis reveals that adolescent birthrates were reduced between 1970 and 1975 as the result of enrollment by teenagers in family planning clinics, independent of the effects of other factors also affecting fertility, such as poverty status, education and urbanization. Using a model which controls for differences in adolescent sexual activity in different areas in 1970 and 1975, the analysis found that for every 10 teenage patients enrolled in family planning clinics in 1975, about one birth was averted in 1976. Other multivariate models, which did not control for differences in sexual activity, showed changes in the same direction, though of smaller dimension. Since the family planning program averts not only births but also pregnancies that result in abortions and miscarriages, an estimate was made of the total number of pregnancies averted by the program. Based on the proportion of unintended pregnancies among adolescents that resulted in live births in 1976 (36 percent), it was estimated that for every 10 teen patients enrolled in 1975, almost three pregnancies were averted in the following year. Over the 1970s, an estimated 2.6 million unintended adolescent pregnancies were averted by the program--944,000 births, 1,376,000 abortions and 326,000 miscarriages. In 1979 alone, an estimated 417,000 unintended pregnancies were prevented by the program.