Filariasis is a tropical disease endemic in many parts of the world that are now inhabited by American troops. In its importance among mosquito borne diseases it looms second only to malaria. However, unlike malaria, the importance of filariasis as a military medical problem has not been fully evaluated as yet because of its long incubation period, estimated to last as long as two years. It is only recently that American military personnel stationed in endemic areas have reached the end of this incubation period. A proper evaluation of the problem should therefore soon become apparent. Filariasis, moreover, may well constitute an important future civilian medical problem. Theoretically, any soldier returning from an endemic area may develop filariasis two years hence when he may well have returned to civilian life. It becomes obvious, therefore, that physicians throughout the United States may be called on to recognize early manifestations of filariasis.