In many endemic communities 40-60% of all adult males have hydrocele. It often develops in the absence of overt inflammatory reactions. Many patients with hydrocele also have microfilarias in the circulation. In bancroftian filariasis, the scrotal lymphatics are the preferred site for localization of the adult worms, and their presence stimulates the proliferation of lymphatic endothelium. The localization of adult worms in the lymphatics of the spermatic cord leads to a thickening of the cord. The hydroceles can become massive, but still occur without lymphedema or elephantiasis developing in the penis and scrotum, since the lymphatic drainage of these tissues is separate and more superficial.