The correlations between malnutrition, parasitosis (especially helminth infections), and child development are complex, and studies of these interrelationships will allow health agencies to maximize screening and intervention strategies for developing countries. We examined these correlations in a cross-sectional program in Carazo State, Nicaragua. Nine hundred sixty-one children in two age strata (ages 0-24 months and ages 2-10 years) from one urban and three rural communities were screened for intestinal parasites (direct smear and ZnSO4 flotation), malnutrition, and developmental delays. Nutritional status was determined as weight-for-age (WFA), weight-for-height (WFH), and height-for-age (HFA). Developmental status (normal, suspect) was determined for the four subtests of the Denver II Screening Test. The prevalence of malnutrition was 14.6% (WFA), 8.4% (WFH), and 36.3% (HFA). Parasitosis was more prevalent in children less than 24 months of age with low HFA, whereas in older children low WFA was more closely associated with parasitic infections. Ascaris and Trichuris were more prevalent in malnourished children. On the Denver II, suspect test results in all four categories (language, social, gross motor, and fine motor) were associated with low WFA, and suspect language tests were associated with both intestinal parasites (P = 0.0003) and Ascaris infection in particular (P = 0.044). Developmental disabilities are a significant and frequently undetected health problem in developing countries, and malnutrition associated with intestinal helminth infections may be an important contributory factor for these disabilities.