In an 18-month period, 3 cases of sphenoidal mucocele following pituitary surgery were diagnosed at our institution. Only 1 case of this late-onset disorder has yet been reported as a pitfall of the transsphenoidal route. Symptoms include recurrent headache and visual complications. Diagnosis was delayed because of misinterpretation of the magnetic resonance imaging findings, which actually showed the development of a sphenoid mucocele long before clinical symptoms occurred. These 3 cases suggest that attention should be focused not only on the sella turcica, but also on the sphenoid sinus, in analyzing the magnetic resonance imaging data. The treatment consists of endoscopic transnasal marsupialization, since the mucocele is lined by normal epithelium with an inflammatory reaction that will heal with drainage. At the time of surgery, prevention would require either endoscopic control of the mucosal remnants, in case of sinus exclusion, or leaving the sphenoid sinus air-filled under a sealed sella.