Allergy to milk has an estimated incidence of 2.5%. Hypoallergenic milks are partial hydrolysates of proteins with lactose. Extensive hydrolysates of casein are mainly small peptides and do not include lactose in their formula. A primary allergenicity as well as a cross-sensitivity are shown for all partial hydrolysates. Even extensive hydrolysates have a weak potential of cross-allergy. The prevention of cow's milk allergy in infants at peculiar risk, born from atopic parents, is based on breast-feeding and/or partial or extensive hydrolysates. There is no conclusive evidence for the usefulness of eviction of dairy products during pregnancy or during the period of breast-feeding. The treatment needs exclusively extensive casein hydrolysates ensuring a 90% protection with 95% confidence intervals. Predictive prick tests in certain cases may help the choice of another hydrolysate. Severe cases with failure to thrive or multiple food intolerance require an amino-acid based formula (Neocate). A rational diversification of the diet is advised in order to prevent the onset of a multiple food intolerance syndrome which could avert from the recovery of cow milk allergy.