The prevalence and intensity of Schistosoma mansoni infections were studied in 3 endemic communities in north-western Ethiopia using the Kato-Katz stool examination technique to determine changes in the epidemiology of schistosomiasis in the absence of control programmes. The prevalence declined in Chwahit community by 21.6%, and in the villages of Jenda and Guramba by 43.2 and 100% respectively in the course of 15 years. This spontaneous reduction in schistosomiasis is perhaps the result of recurrent drought in the area. This finding has implications for public health programmes in the area and intervention measures against schistosomiasis.