Brugia malayi and Wuchereria bancrofti infections cause lymphatic filariasis in Malaysia. About 2.5 million people live in endemic areas of filariasis, of whom 5% have microfilaraemia and probably twice as many are infected. There is a wide clinical spectrum of response to the infection. While some have asymptomatic microfilaraemia, others have episodic attacks of fever, lymphadenitis, retrograde lymphangitis and lymphoedema. Elephantiasis is a late complication. Tropical pulmonary eosinophilia and other forms of occult filariasis are due to hyper allergic reactions to microfilarial antigens. Parasitological and serological tests aid in confirming the clinical diagnosis. The drug of choice is diethylcarbamazine citrate.