A comprehensive review of the uses and interpretation of anthropometric references undertaken by WHO in the early 1990s concluded that new growth curves were needed to replace the existing international reference. To develop new standards, a multi-country study was carried out to collect primary growth data and related information from 8440 healthy breastfed infants and young children from diverse ethnic backgrounds and cultural settings (Brazil, Ghana, India, Norway, Oman and the USA). The first set of growth standards (length/height-for-age, weight-for-age, weight-for-length, weight-for-height and body mass index-for-age) are presented in this report. The curves represent the best description of physiological growth for children under five years of age. The standards depict normal early childhood growth under optimal environmental conditions and can be used to assess children everywhere, regardless of ethnicity, socioeconomic status and type of feeding. This report will be useful to paediatricians and other healthcare providers, nutritionists, policy makers, researchers, national institutes of health, schools of medicine, and professional associations.