OBJECTIVE Tension pneumocephalus is a rare but well-described complication of transsphenoidal surgery. It is usually associated with postoperative cerebrospinal fluid fistulae causing lower intracranial pressure, with air located in the subdural, subarachnoid, or intraventricular space. We report a case of suprasellar tension pneumocyst that caused visual deterioration to develop after an operation for a Rathke's cleft cyst. Only one similar case has been reported previously. METHODS A 54-year-old woman with a cystic sellar-suprasellar mass compressing the chiasm was operated on via a standard transsphenoidal approach. The intraoperative diagnosis was Rathke's cleft cyst, and the floor of sella was left open to avoid recurrence. The sphenoid sinus was filled with a fat graft, and the rostrum of the sphenoid was reconstructed with a bone fragment. The patient's postoperative course was uneventful, and her vision improved. Ten days after discharge, the patient was readmitted to the emergency service with headache and visual impairment. Emergent computed tomography confirmed a suprasellar tension pneumocyst. METHODS The patient underwent immediate reoperation via an endonasal endoscopic approach. After the trapped air was evacuated, the sella was closed with fascia lata and muscle using fibrin glue. The patient's vision improved postoperatively. CONCLUSIONS Suprasellar tension pneumocyst is an extremely rare complication of transsphenoidal surgery. To avoid this complication, the sellar floor should be repaired in a watertight fashion, and patients should be instructed to avoid blowing the nose, sneezing, straining, and coughing postoperatively.