THESE five cases are reported, first, because of the close similarity of the x-ray and wide divergence of the clinical findings; second, to emphasize the value of co-ordinating the history and clinical findings in the interpretation of x-ray evidence, and third, because of the comparative rarity of some feature of each of these cases. Three patients are from the Presbyterian Hospital of the City of Chicago, and two from the Central Free Dispensary of Rush Medical College of the University of Chicago. All of the patients are children, ranging in age from six months to four and one-half years. Their x-ray films show on the shaft of long bones a fusiform elevation of periosteal new bone with dense, sharply defined calcification at the outer margin, which gradually decreases in density to the shaft. The bone shaft is distinctly visible and shows only slight change from normal. The lesions extend either a part or the entire length of the shaft. In four cases the lesions are multiple. In the differential diagnosis of these cases from an x-ray standpoint, one must consider some process which is found in children, and which will elevate the periosteum. Hemorrhage or pus beneath the periosteum, such as can occur from trauma, scurvy, or osteomyelitis, a syphilitic or a rachitic periostitis, occasionally tumor, and more rarely tuberculosis, are lesions of this type. Case 1. This is a white male child, six months old. A film of the right arm shows on the humerus a fusiform elevation of periosteal new bone from one epiphyseal line to the other, rising to a maximum height of one centimeter above the shaft. The calcification beneath the periosteum is homogeneous in character and gradually fades out toward the shaft, which is well defined and slightly more dense than normal. The bones of the forearm are atrophic, otherwise normal. There is swelling of soft tissues of the upper part of the arm. From the x-ray film alone, scurvy, rickets, and probably syphilis can be ruled out because the lesion involves only one bone. Trauma rarely makes such marked changes without definite evidence of a fracture, which is lacking here. The lesion is rather old, as the new bone is fairly dense, and also the shaft is dense, which suggests that it is sequestrated. Two points are uncommon for osteomyelitis: one, the very young age of the patient; the other, the sequestration of an entire shaft without irregular efosion of the shaft. The history was that, at three months of age, the child had whooping cough followed by a left-sided pneumonia. While recovering from the pneumonia, the right arm became swollen and tender, and after two days was incised near the shoulder. The swelling subsided and a discharging sinus persisted. After ten weeks there was a recurrence of swelling and inflammation and increased discharge, at which time the child entered the hospital.