To identify the corresponding cord segment for each root at the level of conus medullaris, a dissecting microscopic study was carried out on the spinal cord of 14 adult cadavers. We measured following contents:1) the longitudinal extent of the medullary segment of origin of each root:2) the distance from the lowest rootlet of the conus to the highest portion of the medullary segment of each root:3) the distance from the conus tip to the lowest portion of the medullary segment of each root:4) the morphological features of root-spinal cord juncton, intrathecal anastomoses, and others. We measured on the basis of the last rootlet ecause of no clear distinction between the conus and filum terminale. Our values showed considerable variation from one case to another. The average length of the whole lumbar and sacral segment was 50 mm and 30 mm, respectively. The S-1 root was the largest. Intrathecal intersegmental anastomoses were found in all cases examined, and usually consisted of small caliber rootlets connecting the spinal roots of adjacent segments. We emphasize the importance of microsurgical structure of conus medullaris when performing an operation of dorsal root entry zone or myelotomy for the relief or spasticity or intractable pain of lower extremities.