Background: A study on foramen magnum morphometry has immense neurosurgical and forensic implications due to its association with myriad intracranial tumours and sexual dimorphism. Aims and Objectives: To study dimensions of foramen magnum in 3-dimensional CT Scans and dry skulls. Methodology: Sagittal and transverse dimensions of the foramen were measured in 50 three-dimensional CT scans and 100 dry skulls. The data obtained was statistically analysed using Student’s t-test for significance, binary logistic regression and ROC curve for sexual dimorphism. Results: The mean sagittal dimension was 32.01 ± 3.92 mm in dry skulls and 33.26 ± 3.86 mm in CT Scans. The transverse dimension was 27.68 ± 2.32 mm in dry skulls and 28.31 ± 2.08 mm in CT scans. In dry skulls mean foraminal area in males was 698.46 mm2 ± 105.32 mm2 and in females it was 590.87 mm2 ± 98.45 mm2. In CT scans it was 705.23 mm2 ± 111.22 mm2 in males and 602.16 mm2 ± 76.23 mm2 in females. The dimensions were significantly more in males than in females and sagittal dimension was observed to have a sex predictability of 67.8%, transverse dimension 62.6% and area 69.7 %. Conclusion: The foramen magnum exhibits sexual dimorphism and is a marker for forensic sexing.A knowledge of shape and dimensions of foramen magnum has diverse neurosurgical implications owing to its proximity to hypoglossal canal, medulla oblongata, pons, spinal cord, cerebellum and related intracranial tumours.