Nutritional rickets was diagnosed in 18 infants aged eight to 24 months. Clinical features included progressive leg bowing, poor linear growth, a diet deficient in vitamin D, seizures, and abnormal serum calcium, phosphate and alkaline phosphatase levels. Wrist radiographs and serum alkaline phosphatase levels were the most useful confirmatory tests. Breast milk may not contain enough vitamin D to protect infants, particularly dark-skinned children and those living in cloudy, northern U.S. cities, from rickets after six months of age. As breast feeding becomes more widely practiced, care is required to ensure that infants at high risk for rickets receive appropriate vitamin D supplementation.