A preventive approach to health care in infancy to a large extent has been ignored despite its emphasis in adulthood. Breastfeeding provides infancy with a major health intervention. Recently published data is reviewed and summarized, giving evidence that breastfeeding provides more preventive health benefits than previously expected. Short-term benefits of breastfeeding include improved immunity, fewer gastrointestinal disturbances, allergy prevention, improved cognitive performance, and protection against parasitic enteric infection. Long-term benefits may include obesity prevention and the lowering of serum cholesterol levels in adulthood. Another major incentive for breastfeeding is the dramatic impact on the cost of infant health care. Hospital costs for breastfed infants are significantly lower than for nonbreastfed infants. These savings can be seen in all socioeconomic levels. A multisystem approach for promoting breastfeeding is recommended. Recommended changes include role modeling, education, revisions in hospital policies, supportive job policy, and new legislation that will enable breastfeeding to become established on a widespread basis. Breastfeeding has the potential of becoming a most significant preventive health intervention for infancy.