This report presents the results of an evaluation of a prenatal health education program conducted within a health maintenance organization (HMO) setting. Specifically, the behavioral, birth, and treatment-cost outcomes for 57 women in an experimental group who received individual nutrition counseling and a home-correspondence smoking cessation program were evaluated against the outcomes for 72 women in a control group who received standard prenatal care. In comparison with the controls, a greater percentage of women in the experimental group quit smoking during pregnancy (49.1 percent versus 37.5 percent). Of those who smoked throughout their pregnancy, women in the experimental group had a greater reduction in their mean rate of daily smoking. A significantly greater percentage of experimental group women adjusted their diets during the prenatal period (91 percent versus 68 percent), and particular success was achieved in increased consumption of dairy products and vegetables, decreased consumption of coffee, and adequate weight gain during pregnancy. Analysis of birth outcome data revealed that infants born to the experimental group had a significantly higher mean birth weight than infants born to the controls (121.34 oz versus 113.64 oz). The experimental group also had fewer low birth weight infants (7.0 percent versus 9.7 percent for controls). Hospital treatment cost savings associated with the reduced incidence of low birth weight infants among experimental group women yielded an overall benefit-cost ratio for the prenatal program of approximately 2:1.