Background: Lesions of fibrous dysplasia involving the spine and scoliosis are thought to be uncommon entities in patients with polyostotic fibrous dysplasia and McCune-Albright syndrome. By examining bone scans of a relatively large cohort of patients with these disorders, we sought to determine the prevalence of spinal involvement and any association with scoliosis. Methods: Sixty-two patients with polyostotic fibrous dysplasia were studied. There were twenty-three male and thirty-nine female patients, and they had a mean age of twenty-five years (range, four to eighty years). Technetium-99m-methylene diphosphonate (MDP) bone scans of the patients were evaluated for evidence of increased uptake in the spine. The presence or absence of scoliosis or a level pelvis and the distribution of other lesions in the skeleton were noted. Results: Thirty-nine (63%) of sixty-two patients were found to have seventy-six lesions of fibrous dysplasia in the spine. Fifty-four lesions (71%) demonstrated increased uptake in the posterior aspects of the spine. Most lesions were located in the lumbar spine (thirty-two lesions) and the thoracic spine (twenty-seven), with less frequent involvement in the sacrum (ten) and cervical spine (six). Twenty-five (40%) of the sixty-two patients had scoliosis; seventeen had a thoracolumbar curve; six, a lumbar curve; and two, a thoracic curve. Seven patients had curves that could not be accurately measured by bone scanning and, therefore, could not be classified. Thirty patients (48%) had no evidence of scoliosis. Thus, the prevalence of scoliosis in patients with polyostotic fibrous dysplasia was between 40% and 52%. There was a strong correlation between spinal lesions and scoliosis (p < 0.001) and pelvic asymmetry (p < 0.05). Back pain was an uncommon symptom. Two patients had a neurologic abnormality; neither abnormality was related to the location of the lesions or the curve. Conclusions: Spinal lesions and scoliosis may be more common in patients with polyostotic fibrous dysplasia than has been previously reported. Since there is a strong correlation between a spinal lesion and scoliosis, these patients should be screened clinically for scoliosis. Level of Evidence: Prognostic study, Level II-1 (retrospective study). See Instructions to Authors for a complete description of levels of evidence.