The relationship between duration of breast-feeding and growth was investigated in a cross-sectional study of children living in an economically disadvantaged rural area of Hubei province, China. Data were analyzed from 2148 children, aged 12-47 months, who had been breast-fed for at least 10 days. 62% of the children had been breast-fed for at least 12 months. The Z scores for weight-for-age, height-for-age, and weight-for-height were computed for each child from National Center for Health Statistics (NCHS) reference data, and the parents completed a detailed questionnaire containing 36 questions relating to socioeconomic, dietary, and medical background. Multivariate regression analysis explored relationships between duration of breast-feeding and anthropometric status. The adjusted height-for-age, weight-for-age and weight-for-height Z scores were significantly greater in children who had been breast-fed for either 12 months or 18 months, compared with those breast-fed for shorter periods. The positive association between duration of breast-feeding remained after adjusting the data for 11 potentially confounding factors. Mean height-for-age decreased with increasing age, was significantly related to birth weight, and was lower in children who had been introduced to less than 3 food groups by 12 months, had a recent infective illness, and whose fathers were farmers. Mean weight-for-age decreased with increasing age, was significantly related to birth-weight, and was lower in children who had a recent illness and whose mothers had no primary education. Mean weight-for-height increased with increasing age, was correlated with birth-weight, and was lower for children with recent infections. Mothers in developing countries should be encouraged to breast-feed their children for the first 2 years of life with the addition of good quality weaning foods from about 4-6 months.