Anisocoria observed under anaesthesia is an alarming sign for anaesthesiologist and is suggestive of possible of neurological involvement due to raised intracranial pressure, intracranial hemorrhage, or space occupying lesions. We report the occurrence of new onset anisocoria in a patient undergoing video assisted thoracoscopic surgery under anaesthesia. The various etiologies of anisocoria under anaesthesia and their implication have been discussed.