Serpiginous and geographic choroiditis, one and the same disease, is characterized by episodic involvement of the pigment epithelium and choroid. Each new lesion passes through an acute phase into an atrophic and scarring one. We observed 20 patients, some with long-term follow-up; some had eventual widespread involvement of both posterior poles. There was no basis for the disease, and treatment did not affect its course. In the patients with long-term disease there was widespread atrophy of the choroid and pigment epithelium and variable amounts of pigment clumping and subretinal fibrous tissue deposition. In nine patients discrete peripheral patches of atrophy were also found. In some eyes the atrophy at the posterior pole had become so confluent that the condition could have been mistaken superficially for a primary choroidal dystrophy. The uninvolved areas appeared to be normal. The electroretinogram and electrooculogram were only affected when extensive disease was present.