Sphenoid sinus mucocele (SSM) is rare and constitutes 1-2% of all paranasal sinus mucoceles. In general, patients present with symptoms such as headache, swelling of the face, nasal obstruction, proptosis, disturbance of globe movements, diplopia and visual loss. In this article, we present a case of ophthalmoplegia which is diagnosed with rare SSM. A 72-year-old man was admitted with an upper respiratory tract infection and concomitant complaints of low left eye lid, diplopia and retroorbital headache. On examination, there were left ptosis and paralysis in all globe movements except for the outward gaze. The patientÂ’s diplopia increased in downward gaze. Fundoscopy was normal. CT revealed a hypodense mass in the left sphenoid sinus that was compatible with a mucocele of about 3x2 cm. The patient was diagnosed with SSM and we performed emergency surgery. Sphenoid sinus mucoceles are very rare and benign lesions, but they can permanently damage the surrounding vital structures. Patients with headache and cranial nerve pathologies should be suspected of SSM. Surgical treatment of SSM by transnasal endoscopic approach can be preferred because of its ease of application and low morbidity and recurrence rates. Early surgical intervention can prevent the damages that will develop in patients.