From at least as long ago as 1883, when Pastor Malling-Hansen1 of Copenhagen reported his observations on the periodicity in the gains of weight among children who were inmates of an institution for the deaf and dumb, records have been published on seasonal variations in the rate of growth of children, and explanations of the causes have been offered by many authors. The present study was undertaken with the hope of determining whether variations in the gains in weight of children of school age throughout the year appear to follow some biologic law, or result from accidental and possibly controllable factors. Little, if any, doubt can be cast on the observations presented here on the growth of children in the cities of the northeastern part of the United States. During infancy and commonly up to the age of 2 years, healthy children on suitable diets and under good environments,