BACKGROUND: Human infection with Wuchereria bancrofti causes a disabling parasitic disease known as lymphatic filariasis, which is a major public health and socio-economic problem in many parts of the world. At the onset of the study, little was known of the distribution of filariasis and its current importance as a public health problem in Nepal. METHODS: Epidemiological mapping was undertaken to determine the prevalence of infection by Wuchereria bancrofti in 37 districts of Nepal between July to December 2001. The study population above 15 years of age was selected, and the immunochromatographic test (ICT Filariasis) was used to screen for circulating filarial antigen (CFA). RESULTS: The overall prevalence of lymphatic filariasis from a 4,488-sample population was 13% and 33/37 districts were found to be endemic. On the basis of geographical data, the highest number of cases was found at altitudes between 500-700 m; however, a substantial number of infected individuals were found in the highly populated Kathmandu valley, at altitudes between 900-1,500 metres where transmission appears to take place. Prevalence rates above 20% were found in 11 districts (with the highest rate of 40%), 6-19% were found in 15 districts, and 0.1-5% were in 7 districts.Information on people's knowledge, attitudes and behaviour towards filariasis was also collected by means of a structured questionnaire, which is presented and discussed in the study. CONCLUSIONS: This is the most extensive study of lymphatic filariasis undertaken to date in Nepal. The study indicates that the prevalence of infection is far greater that was previously reported and that lymphatic filariasis should be a much higher health priority than currently given.