Osteomas are the most commonly encountered neoplasms of the frontal sinus. Extension of these lesions through the posterior table can result in life-threatening complications. We present the case of a 70-year-old man with yellow nail syndrome who complained of persistent rhinorrhea and the sensation of "sloshing" when moving his head. Radiographic investigation revealed a frontal mucocele that had extended to a dramatic intracerebral pneumatocele. This occurred secondary to a frontal sinus osteoma that had been incidentally noted seven years earlier. Surgical exploration via an osteoplastic flap approach allowed us to excise both the osteoma and the associated pneumatomucocele. The resulting dural defect was resurfaced using a flap of pericranium to facilitate anterior cranialization. The features of this interesting case are discussed as an illustration of the potential complications of frontal sinus osteomas. The literature is reviewed regarding management of these lesions and their complications.