A school survey has been carried out in 1998 on a representative sample of 30 schools to assess the effect of the recent urban growth of Niamey on the urban focus of urinary schistosomiasis. A total of 2,024 10-12 years old children were examined and questioned about their water contacts in Niamey and travels in rural areas during the previous year. Generally the prevalence of S. haematobium was low (16%). This can be explained by the lower exposure in urban areas; by the moderate transmission level in the river and by the low incidence of temporary stays in rural areas. A second survey has been carried out in 2000 in 4 schools of a periurban suburb to study the distribution of parasitological risk at the periphery level. A total of 247 10-12 years old children were examined and questioned about their water contacts. Prevalence of S. haematobium was higher in this suburb (74%) but there was a significant decrease of parasitological indices from periphery to the centre. This change seemed related to differences of exposure with an increasing use of water supply and a decreasing use of irrigation canals for swimming and domestic activities.