The planning status of a pregnancy may affect a woman's prenatal behaviors and the health of her newborn. However, whether this effect is independent or is attributable to socioeconomic and demographic factors has not been explored using nationally representative data. Data were obtained on 9,122 births reported in the 1988 National Maternal and Infant Health Survey and 2,548 births reported in the 1988 National Survey of Family Growth. Multiple logistic regression analyses were employed to examine the effects of planning status on the odds of a negative birth outcome (premature delivery, low-birth-weight infant or infant who is small for gestational age), early well-baby care and breastfeeding. The proportion of infants born with a health disadvantage is significantly lower if the pregnancy was intended than if it was mistimed or not wanted; the proportions who receive well-baby care by age three months and who are ever breastfed are highest if the pregnancy was intended. In analyses controlling for the mother's background characteristics, however, a mistimed pregnancy has no significant effect on any of these outcomes. An unwanted pregnancy increases the likelihood that the infant's health will be compromised (odds ratio, 1.3), but the association is no longer significant when the mother's prenatal behaviors are also taken into account. Unwanted pregnancy has no independent effect on the likelihood of well-baby care, but it reduces the odds of breastfeeding (0.6). Knowing the planning status of a pregnancy can help identify women who may need support to engage in prenatal behaviors that are associated with healthy outcomes and appropriate infant care.