Ninety-three clinically and radiologically diagnosed cases of periostitis ossificans were gathered over a 13-year period. Histologic specimens were available in 19 cases. The predominant age, race, and gender were determined. The position of the periosteal reaction, its average length and width, and radiographs required to best demonstrate it were also established. Sequestra were present in two thirds of the cases. Radiographic features and associated clinical findings are described.