OBJECTIVE To report on the clinical characteristics and treatment outcomes of cytomegalovirus (CMV) retinitis cases that occurred after allogeneic hematopoietic stem cell transplantation (HSCT) using an alemtuzumab-based (Campath-1H, Genzyme, Cambridge, MA) conditioning regimen. METHODS A retrospective noncomparative interventional case series. METHODS Seven eyes of 4 patients in whom CMV retinitis developed after allogeneic HSCT using alemtuzumab. METHODS A retrospective chart review was performed. CMV retinitis was diagnosed by the presence of characteristic ophthalmoscopic findings and confirmed by polymerase chain reaction-based detection of CMV in vitreal biopsy specimens. The affected eyes received intravitreal injections of 2 mg/0.1 mL of ganciclovir twice weekly during induction therapy until the lesions were inactive, followed by weekly injections as maintenance therapy. Maintenance intravitreal therapy continued until the lesions consisted of an atrophic retina with pigment epithelium mottling and attenuated vessels. METHODS Visual acuity, response of retinitis lesions, and postoperative complications. RESULTS From 1999 to 2007, 294 patients received allogeneic HSCTs at our institution. Among the HSCTs, 65 were unrelated transplants, and of these, 17 were performed using alemtuzumab-based conditioning regimens. Only 4 patients went on to develop CMV retinitis. These 4 patients had several features in common. All patients received transplants from unrelated donors after an alemtuzumab-conditioning regimen for acute leukemia. One patient died before initiation of treatment. Three patients exhibited a bilateral disease, and 3 patients had neutropenia. Patients underwent a mean of 8.3 intravitreal ganciclovir injections in each eye. All 3 treated patients showed a good response. The treatment was well tolerated without serious adverse events during the mean follow-up period of 8.5 months (range, 4.5-16 months). CONCLUSIONS An increased incidence of CMV retinitis was noted in unrelated patients undergoing HSCT using a nonmyeloablative alemtuzumab-based conditioning regimen. Intravitreal ganciclovir therapy seems to be an acceptable therapeutic option in these patients given the nature of their systemic illness, which prohibits the use of typical systemic anti-CMV drugs.