Primary leptomeningeal gliomatosis is rare, and the diffuse form (PLDG) is even more unusual. The following report is an example. A 17 year-old man developed a syndrome characterized by extensive basal and chronic spinal meningitis. Routine biological tests showed elevated levels of CSF proteins, and moderate mononuclear pleocytosis, with no direct evidence of neoplasia, leading to a diagnosis of chronic meningitis. A second meningeal biopsy, guided by MRI and performed in the left frontal region, led to the specific diagnosis of primary diffuse leptomeningeal gliomatosis. Treatment including ventricular and lumbar shunting, a course of cortico-spinal radiation, and three courses of an eight-drug systemic chemotherapy with intrathecal methotrexate lead to complete remission over 15 months. We believe that this is the first report of such a remission in the literature.