A prospective study of 757 adolescents who gave birth to singleton live-born infants was undertaken to assess effects of prenatal care on pregnancy outcome. The analysis indicated that the odds of low pregnancy weight gain for gestation was reduced by a factor of two (odds ratio = 0.50, P <.05) for adolescents with adequate prenatal care; the risk of preterm delivery was reduced with both adequate (odds ratio = 0.34, P <.01) and intermediate prenatal care (odds ratio = 0.46, P <.05). Birth weight was increased by an average of 157 g with adequate care (P <.05) and 107 g with intermediate care (P <.05). After adjusting for pregnancy weight gain and preterm delivery, differences in birth weight were much smaller and no longer statistically significant, suggesting indirect effects of care on birth weight (ie, improvements in weight gain adequacy and in preterm delivery).