Purpose: To describe immune ring (IR) formation as a manifestation of cytomegalovirus (CMV) endotheliitis. Design: Retrospective observational case series. Methods: Review of all consecutive CMV anterior uveitis and endotheliitis patients seen at the Singapore National Eye Centre for the occurrence of an IR. CMV infection was diagnosed by polymerase chain reaction analysis of the aqueous. Results: None of the 72 eyes with CMV anterior uveitis had an IR formation. Four episodes of IR formation were seen in 3 eyes (14.3%) of 21 cases of CMV-positive endotheliitis. All were unilateral and all 3 patients were human immunodeficiency virus negative middle-aged Chinese males. The IR developed 2 to 7 months after occurrence of the endotheliitis and the aqueous was positive for CMV during 2 of the episodes of IR formation. In 2 eyes, the IR occurred at the completion of a course of systemic ganciclovir when the aqueous was negative for CMV. The immune rings resolved with combination therapy of topical prednisolone acetate 0.12% and ganciclovir. Patient 1 had a recurrence of the IR 4 months after stopping treatment but again resolved following treatment with ganciclovir and topical corticosteroids. Conclusion: Corneal immune rings can occur as a result of CMV infection. Hence CMV infection may have to be considered in such cases.