Background:To describe the first case of optic perineuritis because of meningeal involvement of early stage chronic lymphocytic leukemia (CLL).Methods:A case report and review of the literature.Results:A case of unilateral optic neuropathy associated with enhancement of the optic nerve sheath is described in a patient with a prior 2-year history of Rai Stage 0 CLL. Lumbar puncture revealed a lymphocytic pleocytosis. Cerebrospinal fluid flow cytometry revealed a monoclonal expansion of CD5+ B cells compatible with CLL, matching the flow cytometry characteristics of his peripheral blood.Conclusions:Optic perineuritis is often initially diagnosed as optic neuritis, yet the 2 have different etiologies and follow a different clinical course. Orbital MRI with contrast structurally separates the 2, revealing a characteristic pattern of peripheral optic nerve sheath rather than primary optic nerve enhancement. Etiologies of optic perineuritis are varied and include inflammatory, infectious, neoplastic, and toxic entities. Central nervous system (CNS) involvement by chronic lymphocytic leukemia is unusual, but cranial nerve and meningeal involvement have been reported. This case adds central nervous system chronic lymphocytic leukemia to the list of differential diagnostic possibilities for optic perineuritis. It also alerts clinicians to consider optic perineuritis as a potential presenting feature of CNS involvement in otherwise asymptomatic and stable CLL.