The efficacy and safety of rituximab against B-cell lymphomas is well established. However, there has been an increased incidence of infectious complications after rituximab treatment, mostly hepatitis B reactivation and progressive multifocal leukoencephalopathy. This is the case of a 67-year-old patient with primary central nervous system lymphoma, who developed cytomegalovirus meningoencephalitis after receiving high-dose chemotherapy and rituximab. As there was no evidence of lymphoma relapse or additional immunosuppression, besides his previous treatment, an association between rituximab and cytomegalovirus meningoencephalitis cannot be ruled out.