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The foramen magnum (FM) has a vital importance to have a direct view of the vertebral artery, lower cranial nerves, and the brainstem. The morphologic analysis of the FM was studied in 352 occipital bones of adult human skulls by 3D-Doctor V 3.5.050402 Demo version. The perimeter and area of the FM were calculated as 115.6 (SD, 9.9) mm and 829 (SD, 137.7) mm(2), respectively. The FM index was found as 84.02%, and the majority (38.4%) of holes were observed to have a narrow index.The FM was observed to 8 different types. The most frequently observed types were the tetragonal type in 25.66%, and the one formed by the combination of 2 semicircles in 23.28%. The large anterior margin of the FM type, such as types 1, 4, 5, and 6, can be easily performed partially. In the cases of types 2, 3, and 8, the anterior margin was determined as narrow, the resection procedure is completed with more difficulty. In Pearson correlation analysis, it is significant that a statistically strong relation was found between the area and perimeter, and the area and length of FM. This findings suggest that the resection should be started at the anterior margin, just lateral and then extended superolaterally.