Filariasis infections are often neglected, but they are a significant cause of morbidity and mortality in the endemic areas. The species responsible for most clinical cases are Wuchereria bancrofti, Brugia malayi, Onchocerca volvulus and Loa loa. They are widespread in tropical and subtropical areas. For transmission and a full life cycle, they need a vector that includes an arthropod. Inside the human organism, the infective larvae develop into adults. Female adults produce thousands of microfilariae every day that migrate into the blood and inhabit small capillaries. Clinical filariasis affects the subcutaneous tissue and the lymphatic system. Chronic infection leads to significant edema, which most often affects the lower extremities or genitals. The most well-known clinical entity that is caused by filarias is elephantiasis. Onchocerca volvulus and Loa loa also affect the eye, and the infection can lead to significant impairment of visual acuity or blindness. Diagnosis is based on microscopy of blood samples and proof of the presence of microfilariae or mature adults. Serological tests and circulating antigen tests are being developed, but currently they do not represent an adequate replacement for direct microscopy. Filariasis is treated with diethylcarbamazin, ivermectin or albendazole. Infection control is carried out by controlling the reproduction and spread of vectors and annual prophylactic use of drugs in endemic areas.