This study examines the state of mosquito-borne lymphatic filariasis in Madras, Tamil Nadu, in southern India during the 1970s and into the 1980s. In its various forms it remains a public health problem of considerable magnitude in many tropical countries and affects both rural and urban populations [1. World Health Organization (Third Report). Expert Committee on Filariasis. Tech. Rep. Ser. No. 542, p. 7, 1974]. Here problems of delimiting the spatial extent of morbidity in Madras are discussed and sample survey data are examined which suggest that the disease is prevalent throughout the city to varying extents and that community health education is still inadequate.