PIP: In view of the significant and articulate minority view among pediatricians that breast feeding is not "worth the bother" in developed countries, this review of the literature delves into the evidence from both developed and developing countries for the advantages of breastfeeding, both in infants and for long-term health. Infants in developed settings experience twice the hospitalization rate and more severe illness from lower respiratory tract infection, primarily respiratory syncytial virus. In developing countries the mortality risk is 4-fold. for otitis media, the relative risks were 3.3-4.3 for Finnish infants. Bacterial meningitis and/or bacteremia had a 4-fold risk for hospitalization in a Connecticut study, and a 3-fold relative risk in 2 developing country studies. Human milk was the best preventative for bacteremia and necrotizing enterocolitis in prematures in British neonatal units. A 20-fold reduction in neonatal deaths occurred in Philippine study of breastfeeding, especially in low birth weight babies. Diarrhea causes the most infant mortality in developing nations, where bottle-feeding raises rates 14-fold. In the U.S. estimated relative risks is 3.7 for diarrheal mortality. Sudden infant death is about 1/5 less common in U.S. breast fed babies than in bottle fed. There is evidence for better long-term health after breast feeding in disorders such as celiac disease, Crohn disease, ulcerative colitis, insulin-dependent diabetes mellitus, thyroid disease, malignant lymphoma, chronic liver disease, atopic dermatitis, and food allergies. The design of good studies of protection conferred by breast feeding, and the possible modes of action of breast milk are discussed.