Although pregnant adolescents are at high risk of poor birth outcomes, the majority of adolescents go on to have full-term, healthy babies. Data from the National Longitudinal Study of Adolescent Health, a longitudinal study of a nationally representative sample of adolescents in grades 7-12 in the United States who were surveyed from 1994-1995 through 2008, were used to examine the epidemiology of preterm birth and low birth weight within this population. Outcomes of pregnancies were reported by participants in the fourth wave of data collection (when participants were 24-32 years of age); data were compared between female participants who reported a first singleton livebirth at less than 20 years of age (n = 1,101) and those who were 20 years of age or older (n = 2,846). Multivariable modeling was used to model outcomes; predictors included demographic characteristics and maternal health and behavior. Among black adolescents, low parental educational levels and older age at pregnancy were associated with higher birth weight, whereas low parental educational levels and being on birth control when one got pregnant were associated with higher gestational age. In nonblack adolescents, lower body mass index was associated with lower birth weight, whereas being unmarried was associated with lower gestational age. Predictors of birth outcomes may differ by age group and social context.