We report a 37 year-old man with tension pneumoencephalus secondary to frontal sinus osteoma. He had history of headache and left hemiparesia. CT scan revealed a large volume of air entrapped in the right frontal lobe related to an osteoma in the frontal sinus. The osteoma eroded the posterior wall of the sinus and extended into the cranial fossa. We resected the osteoma throw supraorbital craniotomy, close the dura with temporal fascia, close the bone defect with diploe and put periostium above the bone.