This article presents an unusual case of idiopathic bone cavity that originally was either not observed or diagnosed as a fibro-osseous condition. When a differential diagnosis was established, it included fibro-osseous conditions, odontogenic cysts and neoplasms, and central giant cell granuloma but not the definitive diagnosis. The patient's demographic data, history, symptoms, and clinical and radiographic appearance all conspired to obscure the true nature of the condition, which was not revealed until a biopsy was attempted. A more thorough initial radiographic examination might have led to an earlier diagnosis.