The foramen Magnum is a large opening in the occipital bone of the cranium. The dimensions of the foramen magnum are clinically important because vital structures passing through it may endure compression such as in cases of foramen magnum herniation, foramen Magnum meningiomas and foramen magnum achondroplasia. We studied one hundred dry, adult human skull of unknown sex and measured antero- posterior and transverse diameter with the help of vernier caliper. Additionally surface area of foramen magnum was also calculated. The mean antero-posterior diameter of the foramen magnum was 40.2mm(range 26-40mm) and the transverse diameter was 28.29mm(range 21.5-33.5mm). The mean surface area of foramen magnum was 755.37mm.The knowledge of dimensions of foramen magnum will be helpful radiological diagnostic procedures and neurosurgical procedures to approach in the region of Foramen Magnum. Considering above mentioned importance, this study is worthwhile. The foramen Magnum(FM) (Latin: 'great hole') is a large opening in the occipital bone of the cranium. Its transverse diameter is rather less than one third of the distance between the mastoid processes. The anterior border of the foramen magnum is formed by basilar process of the occipital bone, the lateral border by the left and right ex- occipitalis and posterior border is formed by the