A 60 year old white woman progressively developed radicular pain and weakness in both legs. A meningeal carcinomatosis was diagnosed, and an intrathecal chemotherapy with methotrexate (M.T.X.) was begun. A catheter was placed in the frontal horn of the right lateral ventricle. One month later, the patient progressively developed inattentiveness and confusion. The examination showed an abulic-hypokinetic syndrome, and a left hemiparesis. A C.T. scan showed a hypodensity in the frontal-lobe white matter on the right, with contrast enhancement surrounding the region of the catheter. Results of cytologic, bacterial and fungal studies of cerebrospinal fluid were negative. The catheter was removed. The patient was treated with prednisone and she improved. This complication is very rare, and is noticed in only 0.6% of patients who had intraventricular M.T.X. therapy. The cause of this syndrome is a displacement of the catheter into parenchyma. This syndrome is distinct from the other complications (meningoencephalitis, leukoencephalopathy, myelopathy).