Summary1. A consecutive series of 787 babies born at the University Hospital were followed for 12–36 months in order to determine the prevalence of cow's milk allergy (CMA).2. Fifty‐nine babies (7.5%) were shown by repeated challenge to have evidence of CMA.3. The main manifestations of CMA were eczema in 27, recurrent diarrhea in 24, recurrent rhinorrhea in 18, repeated vomiting in 12, recurrent bronchitis in 10, and asthma in 7.4. Thirty‐four babies had two or more allergic problems, e.g., had recurrent rhinorrhea and eczema, or recurrent bronchitis and recur‐rent diarrhea, 25 babies had only one.5. Babies allergic to cow's milk were often allergic to other foods, 20% for example were allergic to soya.6. Twenty‐five babies developed their first symptoms within 7 days of being given their cow's milk formula.7. Seventeen of the babies lost their sensitivity to cow's milk, 10 of these babies were less than 12 months old. Thirty‐eight babies over 12 months of age when last reviewed were still allergic to cow's milk.8. Babies with CMA, as well as those with other allergic problems, attended their doctors on account of illness more frequently than did the non‐allergic babies.9. Allergic disorders were commonest in the parents and siblings of babies with CMA, and least common in the parents and siblings of the non‐al