Aim: To measure optic nerve sheath diameter as a non-invasive tool for monitoring of intracranial pressure during pre-operative, intra-operative and post-operative period in patients with supratentorial intracranial space occupying lesions. Material and methods: The present prospective nonrandomised observational study was conducted in the Department of Neurosurgery, Bangur Institute of Neurosciences & SSKM hospital, IPGME & R, Kolkata from February 2020 to February 2022. Adult patients undergoing operation for supratentorial intracranial space occupying lesions during the time period were included in the study. A total of 50 cases were recruited during the study period. We measured the ONSD in the preoperative, intraoperative and postoperative period. Clinical findings suggestive of raised ICP, Cranial computed tomography or magnetic resonance imaging finding of shift, edema, mass effect, collapse of ventricles, compression of cisterns or effacement suggestive of elevated intracranial pressure was used to evaluate optic nerve sheath diameter accuracy.