Purpose: We present an atypical case of cytomegalovirus corneal endotheliitis after intravitreal triamcinolone injection.Case summary: A 61-year-old man presented with decreased visual acuity after intravitreal triamcinolone (Maqaid®, Wakamoto Pharmaceutical Co., Ltd., Tokyo, Japan) injection for cystoid macular edema following cataract surgery. Ocular examination revealed elevated intraocular pressure, diffuse keratic precipitates with corneal edema, and anterior chamber inflammation. These findings were suggestive of viral corneal endotheliitis. Polymerase chain reaction analysis of the anterior chamber aqueous humor detected cytomegalovirus DNA. Consequently, the patient was diagnosed with cytomegalovirus corneal endotheliitis. He was treated with oral valganciclovir (Valcyte®, Roche, Basel, Switzerland) at a dose of 1,800 mg/day for 3 weeks as an induction phase, followed by 900 mg/day for 3 weeks as a remission phase. This treatment regimen led to significant improvement in corneal edema and anterior chamber inflammation with complete restoration of visual acuity.Conclusions: It is important to note that cytomegalovirus endotheliitis can occur after intravitreal triamcinolone injection and can present in an atypical rather than a typical form.