A 65-year-old woman presented with progressive gait disturbance. She complained of appetite loss for 3 months. Her gait gradually became unsteady, and she was admitted to our hospital. On admission, slow mentation, bathyhypesthesia in left upper and both lower extremites, positive Romberg sign and wide-based gait were observed. Gd-enhanced MRI revealed mass lesions in the left temporal fossa and the cervical spinal canal with focal meningeal enhancement. Besides lesions in the central nervous system (CNS), systematic examination detected no additional malignancy. Repeated cytology of the cerebrospinal fluid was negative. After admission, her consciousness became reduced gradually. At 2 months after admission, she died of central respiratory failure. On autopsy, diffuse extension of the tumor cells was observed on the surface of CNS, and the mass lesions observed by MRI were extra-parenchymal On microscopic examination, the mass was consisted of GFAP positive malignant cells, and included perivascular pseudorosette, pseudopalisading necrosis and many mitotic cells. The diagnosis of the case was made as primary diffuse leptomeningeal gliomatosis (PDLG). PDLG is a rare disorder that is difficult to diagnose by CSF cytology. The progress of PDLG is rapid, and appropriate treatment is rarely taken. However, the combination of temozolomide and the radiotherapy performed for a glioblastoma has been reported as a possible treatment for PDLG. We emphasize that, in possible cases of PDLG, a biopsy should be performed in the early stages, especially in cases showing features similar to those of metastatic meningeal carcinomatosis and have no malignant tumors by whole body examination.