In 1983, 89,000 children were born to United States women aged less than or equal to 16. To reduce teenage fertility rates, public health workers will need to identify teenagers at elevated risk for childbearing. We tested the hypothesis that the sisters of childbearing teenagers may form such a group. We performed an historical cohort study of 3,767 teenagers aged 12-16 years who were enrolled in Arkansas Aid to Families with Dependent Children (AFDC), 1978-81; they had 247 pregnancies. Multivariable log-linear hazard models were used to control and study age, race, number of AFDC-eligibles per household, and county urbanization and family planning services. Teenagers whose sisters bore children had elevated rate ratios (RR) for childbearing (RR = 1.8; 95% Confidence Limits [CL] = 1.2-2.6), as did Blacks (RR = 3.1; 95% CL = 2.0-4.8), and members of households with more than nine AFDC-eligibles (RR = 1.7; 95% CL = 1.1-2.6). Because they may have elevated childbearing rates, and would be easy to contact, the sisters of pregnant teenagers could form an important target population for family planning efforts.