.Helminthic infections among children are subtle and insidious constraints on normal physical development. They impact negatively on children's genetic potential growth, with clinical consequences of iron.deficiency anaemia and other nutritional deficiencies (Awasthi et al., 2003). School-age children are particularly at risk of parasitic infections and under-nutrition, yet they have not been the focus of nutritional surveys. A cross-sectional study was conducted in Nairobi among school children 5-14 years in early 2006 from 39 randomly selected schools. 32 were public, five were private and two were informal schools. Stool samples from 1632 pupils were microscopically examined (Katz et a!. 1972) to establ ish the presence or absence of soil transmitted helminthic eggs and Schistosoma manson; while nutritional status data were analysed for 1574 pupils because their anthropometry data were correctly recorded. i, The prevatenceof .chton ic malnutrition .. (stunting) among the children was determined using Height-for-Age nutrition status indicator while being underweight or overweight was determined using the BMI-for-Age indicator. 12.8% of the children were infected by at least one of the three soil transmitted helminths (STHs) and S. mensoni. 33% were underweight while 10.7% were stunted. Children with parasitic infections were three times more likely to be underweight than those without infections (p>O.OS). Children with over one parasitic infections were 1.6 times more likely to be underweight than those exposed to one type. Exposure to parasitic infection contributes to both underweight and stunting among school children ..