Opportunistic infections of the retina are becoming a more frequent diagnostic and therapeutic challenge as immunosuppressed patients become more common. Viral, fungal, protozoan, and bacterial agents may be encountered. Diagnostic and therapeutic considerations, illustrated by case histories, are presented in this article. Viral infections are characterized by progressive exudation and hemorrhagic necrosis in a segmental distribution corresponding to the retinal vasculature. Protozoan, fungal, and bacterial infections may demonstrate more focal lesions with greater vitreous involvement. Diagnosis is established by clinical examination of body fluids. Antimicrobial drugs alone or combined with vitrectomy are effective therapy for fungal, bacterial, and protozoan infections. Antiviral drugs have yielded more disappointing results in the management of viral retinitis.