Aims and background: Pneumocephalus is a very rare complication after optic nerve sheath fenestration (ONSF). There are various mechanisms by which pneumocephalus can occur. The Dandy's ball valve mechanism defines a one-way movement of air into the cranial cavity produced by positive pressure events like coughing, while Horowitz's inverted soda bottle mechanism explains that air gets sucked into the skull due to pressure gradient triggered by negative intracranial pressure (ICP). In our case, postoperative persistent coughing resulting from postnasal dripping of cerebrospinal fluid (CSF) possibly caused the air to enter the cranial cavity through the surgically created bony defect, leading to pneumocephalus. The patient was managed conservatively with a successful outcome. Case description: A young female in her 30s was diagnosed as a case of idiopathic intracranial hypertension (IIH) with visual disturbances for the last 3 years. She underwent ONSF and postoperatively had pneumocephalus. On postoperative day (POD) 1, she had a headache, fever, and neck stiffness, for which a computed tomography (CT) scan of her head was done, which showed pneumocephalus. She was conservatively managed with intravenous (IV) antibiotics, 100% oxygen and bed rest with headend elevation. At the end of 1 week, her symptoms improved, and a repeat CT scan of her head after 8 weeks showed no pneumocephalus. Her vision had improved from 6/36 in the right eye to 6/6 and from finger counting close to the face in the left eye to 6/18 after surgery. Conclusion: Postoperative pneumocephalus after ONSF, though rare, should be carefully evaluated, and all causes should be mitigated to avoid adverse complications. Clinical significance: The bone over the intracanalicular part of the optic nerve, after being drilled, can act as a pathway between the nasal cavity and intracranial cavity through which air can enter the intracranial cavity, leading to pneumocephalus. Unilateral ONSF can have a beneficial effect on both the eyes and prevent further deterioration of vision.