Many infants are fully or partially breast fed during the early months of life; however, the percentage of such infants decreases to about 30 percent by 4 months of age. The majority of US infants are fed formulas for most of the first 10 months of life. Although fluoride (F) intakes by fully breast-fed infants are low, F intakes by partially breast-fed infants and by formula-fed infants are highly variable, depending primarily on the F content of the water used to dilute concentrated liquid or powdered infant formula products. In communities with F content of the drinking water less than 0.3 ppm, F consumption by many infants will be 30 to 40 micrograms.kg-1.d-1. The addition of a F supplement of 0.25 mg/d for a 4 kg infant would increase the F intake by 63 micrograms.kg-1.d-1, resulting in a total intake of about 100 micrograms.kg-1.d-1, an intake in the range believed to be associated with development of fluorosis of the permanent teeth. However, for the US infant population generally, many fewer infants are exposed to high F intakes from formula plus a supplement (recommended only for communities with water providing less than 0.3 ppm F) than from formula alone in communities with F content of 1 ppm in the drinking water. In assessing the possible effects of F intake during infancy on development of fluorosis, it is important to recognize that infant feeding practices have changed greatly during the past 30 years. In the 1960s, most infants over 4 months of age were fed fresh cow’s milk and intakes of F were therefore low. By the mid 1970s a trend toward more extended feeding of formula was evident and this trend has continued into the 1990s. Prolonged exposure to high intakes of fluoride during infancy is much more common now than in the past.