Encephaloceles usually involve herniation of frontal lobe tissue through an anterior cranial fossa defect into the ethmoid sinus or nasal cavity. Encephaloceles can also result from temporal lobe herniation through a middle fossa defect into the sphenoid sinus. Within the sphenoid, encephaloceles are thought to occur most commonly in the central or midline aspect of the sinus. Lateral sphenoid encephaloceles, especially within the lateral aspect of the sphenoid sinus when the sphenoid sinus has pneumatized extensively into the pterygoid recess, are considered exceedingly rare. The objectives of the study were to review our experience with sphenoid encephaloceles to understand the relative frequency and the locations in which they occur within the sphenoid sinus and to report our experience in caring for patients with this condition. Retrospective review. Retrospective review of patient records and operative reports from 1991 to 2000. RESULTS Twelve patients were treated for intrasphenoid encephaloceles during a 10-year period. Eight patients had lesions located in the lateral recess of the sphenoid sinus. Surgical repair was undertaken in all 12 cases using endoscopic techniques. In 11 of 12 cases, the repair was successful with follow-up times of 12 to 69 months (mean follow-up, 31.9 mo). Temporal lobe encephaloceles in the lateral sphenoid sinus have been reported rarely in the literature. Careful preoperative evaluation and localization of the sphenoid defect are critical for the selection of the optimal surgical approach for repair of the skull base defect. Our 10-year experience represents the largest group of patients treated endoscopically for intrasphenoid encephaloceles reported to date.