WITH THE increasing frequency of the use of high voltage roentgen rays in the treatment of malignant neoplasms, the effects on normal tissue have become increasingly important to the radiotherapist and to the clinician. Not the least important of these effects are the changes occurring in bone and cartilage, although they do not appear to be widely familiar from a clinical point of view. Nevertheless, changes occurring in bone as a result of irradiation therapy have been reported since 1903, and in this paper we wish to review briefly the pathologic process involved and to present 2 cases, 1 of which is the third to be reported involving a male patient, as examples of the pathologic and the clinical importance of postirradiation lesions. Wammock and Arbuckle1quoted Perthes, who described the effects of roentgen rays on epiphysial growth in 1903, and Cluzet, who in 1910 described delay in callus