Monostotic fibrous dysplasia of the spine is rare, with the cases of fewer than thirty-five patients discussed in the literature. Dahlin and Unni reviewed the cases of 418 patients with monostotic fibrous dysplasia and noted six (1.4%) involving the spine1. In a series reported by Harris et al., one patient with spine involvement was noted in a total of thirteen patients with monostotic fibrous dysplasia2. Most reports have described the case of a single patient with minimal to no follow-up1-23. As a result, the natural history and ideal treatment for this condition remain poorly understood. For example, the prevalence of scoliosis in patients with polyostotic fibrous dysplasia has been found to be up to 40%24, whereas scoliosis in monostotic fibrous dysplasia appears to be quite rare25. The reported treatment of monostotic fibrous dysplasia in the spine also has varied widely, from surgical resection4,5,7,9-19 to biopsy and observation2,21. We present the cases of a series of seven patients who were diagnosed with monostotic fibrous dysplasia of the spine at our institution. The history, physical examination, and histologic characteristics are described along with the results of clinical follow-up evaluations. The Massachusetts General Hospital and Partners Healthcare institutional review board approved this study. We utilized our Bone Sarcoma Registry to identify all eleven patients diagnosed with fibrous dysplasia of the spine between 1980 and 2007. The histologic diagnosis of fibrous dysplasia was made on the basis of the appearance of curvilinear trabeculae of woven bone surrounded by a fibrous-appearing stroma composed of spindle cells (Fig. 1). Two patients were excluded because of the presence of polyostotic disease, one was excluded because of the lack of a tissue diagnosis, …