Osteomas are the most common benign paranasal sinus tumors and are often found in the frontal and ethmoidal sinus. Intracranial complications such as pneumocephalus have occasionally been reported in association with osteomas. We describe a 33-year-old man with a large frontoethmoidal osteoma complicated by tension pneumocephalus and neurological disturbances, and we discuss the clinical and imaging resolutions after surgical management. We emphasize the imaging features and neuroendoscopic approach to avoid life-threatening conditions.