Aneurysmal bone cysts of the sphenoid sinus are very rare, with only six cases described in the literature. We present a case of an aneurysmal bone cyst of the sphenoid sinus with associated fibrous dysplasia in which the radiological findings had some features of a mucocoele. We discuss the differences in pathogenesis, clinical presentation and radiological appearances between these two lesions, and propose a simple drainage procedure as an effective modality of treatment.