To describe the demographic profile and clinical and laboratory findings of 248 patients with acquired retinitis caused by systemic infection with toxoplasmosis in a presumed outbreak of the disease. Design: Retrospective observational case series. Results: Most patients (209) were residents of one city in Southern India. A total of 35 patients had a prodrome of fever, and 242 patients had unilateral retinitis without associated old retinochoroidal scars. All had laboratory evidence of acquired systemic infection with Toxoplasma gondii, and all favorably responded to antitoxoplasma therapy. Toxoplasma IgM and IgG antibod-ies were detected, suggesting recently acquired systemic disease. Complications seen were macular scars in 50 eyes (25.1%); epiretinal membranes, 23 eyes (11.5%); cataract, 5 eyes (2.5%); posterior vitreous detachment, 12 eyes (6%); and retinal detachment, 12 eyes (6%). One recurrence has been seen. The suspected source of infection is municipal drinking water. Conclusion: Large numbers of residents of any age in a population are at risk of acquiring ocular disease during an outbreak of toxoplasmosis, which can go unnoticed, and can cause significant ocular morbidity.