Adult lymphatic filariae (Wuchereria bancrofti, Brugia malayi) can cause blocking of lymphatics producing obliterating endolymphitis lesions. The subsequent extravasation of lymph (or chyle when the obstruction is canal) is at the origin of the formation of lymphedema or elephantiasis, in which the main histological finding is great hypertrophy of collagen elements. This theory involving filaria only is not the full picture, and bacterial infection, mainly by streptococci, is an important factor. The association of filaria with microbes is particularly dangerous because the presence of the latter, or its toxins, causes death of local microfilariae and even adult worms, which are known to be more harmful dead than alive. The progression of the disease, especially in cases with lymphedema, which mainly affects the limbs and the genital organs, depends on three factors: the species of filaria, the degree of transmission, and the receptivity of the patient to the parasite. Large differences are found according to the region involved, and in the same endemic zone, according to the individuals affected. However, they almost always occur progressively in areas where there have been recurrent attacks of acute lymphangitis.