Light or moderate intensity infection with Schistosoma mansoni may contribute to growth deficits. We report on the effects of treatment for S. mansoni on growth and development in Brazilian schoolchildren. Anthro pometric measurements were taken from 539 S. mansoni-infected children and their age- and sex-matched egg negative controls between the ages of 7 and 15 years. The children as a whole exhibited chronic malnutrition, with growth retardation in height evident in 21% of the population. Infected children, however, were significantly smaller in height, weight, mid upper arm circumference (UAC), tricep skinfold (TSF), and subscapular skinfold (5SF) mea surements than control children (P < 0.05). These differences were due primarily to a greater disparity between infected and egg-negative girls in height (P < 0.01), weight (P 0.01), UAC (P = 0.02), and TSF (P < 0.01). Nevertheless, girls demonstrated a better level of development and nutrition compared with boys. While infected boys were shorter and weighed less than controls, these differences were not significant. Growth and development in girls was negatively correlated with intensity of infection. Coinfection with S. mansoni and Trichuris appeared to act synergistically in the development of malnutrition.