The effects of maternal age on low birth weight, newborns' hospital costs and infant mortality were estimated based on individual 1989 and 1990 vital statistics records from New Jersey that were linked with uniform billing hospital discharge records. Results of multivariate analyses show a U-shaped relationship between maternal age and low birth weight among whites, with the youngest (younger than 15) and oldest (aged 40 and older) mothers being at higher risk than 25-29-year-olds; older teenagers were not at any significantly increased risk. Among blacks, however, 15-19-year-olds faced significantly lower risks of delivering low-birth-weight babies than did black women aged 25-29. Both black and white mothers in their 30s were significantly more likely to deliver a low-birth-weight baby than women aged 25-29 of the same race. The multivariate analysis also showed that newborn hospitalization costs increased with maternal age among both blacks and whites. The seemingly poorer birth outcomes of teenage mothers appear to result largely from their adverse socioeconomic circumstances, not from young maternal age per se.