To describe an unusual presentation of a primary lymphoma of the central nervous system in a patient who, four months prior to admission, was diagnosed with herpes zoster ophthalmicus (HZO).A 68-year-old man, with a history of HZO, was admitted to the emergency department with nausea and vomiting that had persisted over the previous two weeks. Neurological evaluation showed right ptosis, divergent strabismus and anisocoria. Blood tests showed high c-reactive protein, while serology was negative for human immunodeficiency virus. A brain CT scan revealed three round lesions, slightly hyperdense, periventricular in the occipital and frontal regions, which biopsy revealed to be a diffuse large B-cell lymphoma. The patient started chemotherapy but progression to death was inevitable.The authors describe an unusual presentation of primary lymphoma of the central nervous system and urge physicians to be aware of this presentation in order to avoid misdiagnosis.Herpes zoster ophthalmicus can reflect underlying diseases and lead to misdiagnosis.An occult neoplasm should be considered in an otherwise immunocompetent elderly patient who develops varicella-zoster virus infection.