Polyostotic fibrous dysplasia of the thoracic spine is extremely rare and considered a benign disease. We report the case of a 46-year-old woman admitted to the emergency department for subacute paraplegia. The spinal X-ray showed a spontaneous fracture at the T4-T5 level. The CT scan revealed a tumor infiltration of the vertebral body responsible for lysis. Spinal MRI confirmed the neoplasia also located in the epidural space with spinal cord compression. The patient underwent an emergency laminectomy associated with transpedicular screw fixation between the T2 and T6 levels. At 2 months, she had evolved to a normal gait. In the second session, a transthoracic approach was used for a bone-graft-assisted fusion procedure to achieve long-term stabilization. At 4 years, the bone fusion was excellent and the patient was able to resume socioprofessional activities. The diagnosis of fibrous dysplasia is usually made histologically on surgical biopsy but MRI and CT scan sometimes provide a preliminary indication. Although a consensus for management of this disease has not been achieved, the authors recommend radical removal of all involved tissues accompanied by internal fixation and bone-graft-assisted fusion.