Paranasal sinus carcinoma is rare, with an estimated annual incidence of less than 1 per 100,000 population. Primary frontal sinus involvement is extremely rare, accounting for only 0.3% of all paranasal sinus malignancies. A frontal sinus cancer may be mistaken for a mucocele, pyocele, or osteomyelitis. We report the case of a 48-year-old woman with a carcinoma that originated in the frontal sinus. Computed tomography and magnetic resonance imaging demonstrated bony destruction with intracranial extension but no involvement of the bulbus. The patient underwent a frontal craniotomy, tumor excision, and postoperative radiotherapy. One year later, she remained symptom-free.