OBJECTIVE: To report a case of a patient with aggressive juvenile cemento-ossifying fibroma of the ethmoid sinus and emphasize its surgical importance. CASE REPORT: The patient, GGCL, an 8-year-old boy, from Pindamonhangaba-SP, was referred to our service when he was 4 years old, with a marked proptosis and epiphora in the right eye, but with eye movement preserved. A CT scan of the sinuses showed a tumor in the right nasal cavity. During surgery, a friable lesion, rejecting the ipsilateral orbital wall, extended to the roof of the ethmoid, which was resected endoscopically with neuronavigator assistance and histopathological diagnosis of juvenile cemento-ossifying fibroma. Meningoencephalocele and fluid leak from the ethmoid were corrected endoscopically successfully in May 2010. After 3 years, the tumor had affected the entire right nasal cavity. An endoscopic approach was adopted using the neuronavigator. The patient is continuing postoperative follow-up without complications. CONCLUSION: Cemento-ossifying fibroma is a rare benign tumor of the nasal cavity and paranasal sinus, and is easily misdiagnosed. It can be seen in any other craniofacial region, but generally in the maxilla and mandible. The average age at diagnosis is the third and fourth decades, and this condition occurs predominantly in women. The case differs from the literature because the premature involvement and aggressiveness forward recurrence, featuring a poor prognosis. Surgical planning and appropriate follow-up are the main measures to avoid possible complications, and the only solution is to perform complete resection of the tumor.