An estimate of the number of schistosomiasis infections in Cameroon was based on a statistically representative national prevalence survey carried out in the entire country. The number of cases of infection by Schistosoma haematobium was estimated to be 393,900, and 419,600 for S. mansoni, a total of 813,500. Taking into account the dual infections the total number of cases was 719,100 (95% confidence interval: 392 900-1 027,800). A current World Health Organization estimate extrapolating from the results of limited epidemiological surveys showed 2,239 591 cases for Cameroon, an estimate 3.1 times higher than the more accurate estimate based on the national survey. Schistosomiasis being a focal disease, prevalences observed in limited foci are not representative of regional prevalences. Prevalence survey data in the literature are biased toward reporting only positive results. Therefore extrapolations made on limited surveys may lead to an overestimation of the number of cases of schistosomiasis.