The association between schistosomiasis japonica and child growth was studied cross-sectionally in 1,561 males and females aged 4-19.9 years residing in an endemic region of northeastern Leyte, The Philippines. Stature, weight, upper arm muscle area, and sum of triceps and subscapular skinfold thicknesses were measured and related to presence of Schistosoma japonicum eggs in Kato stool smears and to the intensity of infection assessed by quantitative egg count. The presence of hookworm, ascaris, and trichuris eggs was also measured. Multivariable models were used to control for the effects of age, age2, and polyparasitism on growth. The prevalence of schistosomiasis was 31% in males and 22% in females, with the maximum prevalence in adolescence. In 8-19-year-old subjects, the intensity of schistosomiasis japonica was significantly related in males to reduced arm muscle area and sum of skinfolds (both P less than 0.01) and in females to reduced stature, weight, arm muscle area, and sum of skinfolds (all P less than 0.01). The greatest age-specific differences were during adolescence in both males and females. The growth retarding effects of intensity of schistosomiasis japonica were independent of the influence of other parasites, notably hookworm. Due to the magnitude of the schistosomiasis-associated growth differences in adolescence, adult body size, function and productivity may be affected.