A 33-year-old male presented with a complaint of intermittently blurred vision and right facial weakness. MRI of the brain and orbits revealed numerous cranial nerve abnormalities. There were no focal brain or spinal cord lesions. Cerebral spinal fluid flow cytometry revealed a monoclonal population of B-lymphoid cells. No other evidence of disease was found. Serum Lyme antibody was reported to be IgM positive. Therapy with ceftriaxone, was followed by improvement in his symptoms. Although flow cytometry is a useful tool in distinguishing malignancy from inflammatory disorders it does not always establish the diagnosis of malignancy by itself.