Thirty-four patients with florid osseous dysplasia were studied. The majority were asymptomatic Negro women: Seventeen biopsy-proven simple bone cysts were found in affected quadrants of fourteen patients. Radiographs displayed a spectrum of sclerotic and ground-glass opacities limited to alveolar processes but not to root apices. Biopsy material was studied in all cases, and biochemical analyses of serum and cyst fluid were performed on some patients. Test results and skeletal radiographs indicate that the disease is limited to the jaws. Patients have remained asymptomatic with little alteration of radiographic patterns. Three cysts failed to heal following treatment, others filled with radiographically abnormal tissue. Chronic osteomyelitis may infrequently complicate the disease. These cases appear to represent the most exuberant manifestation of this reactive fibro-osseous jaw disease.