Cytomegalovirus (CMV) retinitis, a common complication of the acquired immunodeficiency syndrome (AIDS), is increasing in frequency as patients infected with the human immunodeficiency virus (HIV) live longer. In recent years, the lifetime risk for CMV disease in HIV-infected persons has increased from 24.9% to 44.9%. Cytomegalovirus retinitis is usually diagnosed clinically: Almost all patients are CMV seropositive and have CD4+ counts less than 50 cells/mm3. Specific diagnostic tests that use antigen detection or quantitation of circulating nucleic acid to detect CMV are being developed, but they have not been validated for routine clinical use. Such tests would help predict disease, diagnose acute retinitis, and monitor therapy. Therapy with systemic agents, including intravenous ganciclovir, intravenous foscarnet, and intravenous cidofovir, is effective. However, it is cumbersome, costly, and associated with considerable toxicity, therapy encouraging investigation of other therapeutic approaches. Intravitreous injections with antiviral agents are effective, but the short half-life of available agents makes these injections inconvenient. Intraocular implants that slowly release ganciclovir have been effective for both acute therapy and long-term maintenance, but they need to be directly compared with intravenous and oral regimens to determine which regimen will optimally maximize convenience, preserve vision, and improve survival. Cytomegalovirus retinitis could be prevented by improved antiretroviral therapies or by immune-based therapies that would prolong the time during which patients remain immunocompetent. Once patients become immunologically susceptible to CMV end-organ disease (when their CD4+ counts decrease to < 50 cells/ mm3), specific chemotherapy with oral ganciclovir is promising, but the cost, inconvenience, toxicity, and conflicting reports of efficacy associated with this strategy mean that it needs careful assessment before it can be considered standard treatment. Management of CMV retinitis is on the verge of major changes. In the next few years, improvements in diagnostic, therapeutic, and preventive tools should reduce morbidity and mortality from this disease.