The SAPHO (synovitis, acne, pustulosis, hyperostosis, and osteitis) syndrome includes a complex group of disorders characterized by peculiar bone lesions, most commonly involving the anterior chest wall, and sometimes accompanied by dermatologic manifestations. The clinical and radiographic features of this syndrome are well described, but few studies have examined the histologic features of the bone lesions. We describe the clinical, radiographic, and histologic features of the osseous lesions encountered in eight patients with a clinical diagnosis of SAPHO syndrome. The patients included five female and three male patients ranging in age from 5 to 63 years (mean, 35.3 years). The most common clinical presentation was pain related to the sites of osseous involvement. Two patients also had some form of pustular dermatosis. The radiographic features of the osseous lesions varied but often suggested the possibility of a neoplasm. Nine pathologic specimens were available for review, five from the clavicle, two from the first rib, one from the calcaneus/cuboid, and one from the tibia. The histologic features varied but seemed related to the duration of the patients' musculoskeletal symptoms. Early lesions contained acute inflammation, edema, and prominent periosteal bone formation, histologically indistinguishable from ordinary bacterial osteomyelitis, whereas late lesions demonstrated markedly sclerotic bone trabeculae with prominent marrow fibrosis and only mild chronic inflammation; one of these biopsies appeared virtually identical to Paget's disease. One biopsy was performed after an intermediate duration of symptoms and contained prominent chronic inflammation only. The histologic findings in SAPHO are variable and nonspecific and may depend on the duration of disease, but it is important to recognize the spectrum of histologic changes possible in the syndrome and to realize that clinicopathologic correlation is necessary to avoid misdiagnosis and unnecessary long-term antibiotic therapy.