Monostotic fibrous dysplasia involving the spine is rare. There have been only 6 previous reports of monostotic fibrous dysplasia involving the thoracic spine and none had malignant transformation. We report a case of monostotic fibrous dysplasia of the thoracic spine with malignant transformation. Findings on plain radiographs, isotope bone scan, computed tomography and magnetic resonance imaging are discussed and compared with those of the previously reported cases.