We evaluated a comprehensive program of prenatal and postpartum nurse home visitation. The program was designed to prevent a wide range of health and developmental problems in children born to primiparous women who were either teenagers, unmarried, or of low socioeconomic status. During pregnancy, women who were visited by nurses, compared with women randomly assigned to comparison groups, became aware of more community services; attended childbirth classes more frequently; made more extensive use of the nutritional supplementation program for women, infants, and children; made greater dietary improvements; reported that their babies' fathers became more interested in their pregnancies; were accompanied to the hospital by a support person during labor more frequently; reported talking more frequently to family members, friends, and service providers about their pregnancies and personal problems; and had fewer kidney infections. Positive effects of the program on birth weight and length of gestation were present for the offspring of young adolescents (less than 17 years of age) and smokers. In contrast to their comparison-group counterparts, young adolescents who were visited by nurses gave birth to newborns who were an average of 395 g heavier, and women who smoked and were visited by nurses exhibited a 75% reduction in the incidence of preterm delivery. (P less than or equal to .05 for all findings.)