The present case shows the usefulness of cerebrospinal fluid (CSF) cytology in the diagnosis of leptomeningeal dissemination by immature teratoma. The tumor arose in the thoracolumbar spinal cord of a 14-year-old male. The initial histopathologic diagnosis was made on the tumor tissue taken at laminectomy. Postoperatively, CSF cytology revealed epithelial cell clusters, scattered squamous epithelial cells and small bundles of striated muscle fibers in the background of many histiocytes and inflammatory cells. Although these cells showed only slight cytologic atypia, their presence in the subarachnoid space suggested the leptomeningeal spread of well-differentiated portions of the immature teratoma. The postmortem examination revealed the primary tumor in the spinal cord and multiple metastatic nodules in the brain.