A patient with the prolymphocytic variant of B cell chronic lymphocytic leukemia (CLL/PL) who developed meningeal leukemic involvement is reported. He had been diagnosed as having CLL/PL 2.5 years earlier, and treated successively with splenectomy, continuous chlorambucil and CHOP chemotherapy. While receiving the latter treatment, the patient developed persistent cephalalgia and vomiting, without signs of neurological focality. A lumbar puncture yielded a cerebrospinal fluid (CSF) showing lymphoid cells of prolymphocytic appearance and the immunological cell markers demonstrated the clonality of these cells. Intrathecal methotrexate and arabinosyl cytosine treatment was administered, this leading to the disappearance of the abnormal cells from the CSF and the resolution of the clinical symptoms.