This report is concerned with the treatment of radiation skin ulcers with alpha particles from radon. The utilization of alpha-radiating agents in post-irradiation ulcers was first suggested in 1925 by Fabry (1–3), who used Thorium X in concentrations from 1,500 to 2,000 electrostatic units per gram vaseline base. The ointment was left in place two to three days, and the treatment was repeated after three to six weeks. The favorable results reported by Fabry were confirmed by Delmes (4), who employed considerably smaller doses (20 e.s.u.). Jessner (5) obtained similarly good results using an ointment containing Thorium X marketed under the name of Doramad and containing 2,000 e.s.u. per gram of ointment. The most extensive studies in the treatment of post-irradiation skin reactions with alpha radiation are those of E. Uhlmann (6–13) undertaken in 1929. The encouraging clinical results demonstrated by Uhlmann convinced us that this method of treatment deserved further study. Skin changes following radiation therapy have become more common in recent years. The reason for this increased frequency is the far more intensive irradiation employed in the last two decades. The cutaneous reactions which occur as immediate sequelae of treatment, erythema and radio-epidermite, are anticipated as the result of intensive irradiation, while reactions which occur after an interval of about six months are unpredictable. When late sequelae of intensive irradiation occur, they vary considerably in their degree of severity. In the order of frequency of occurrence, they are patchy pigmentation, depigmentation, atrophy, telangiectasia, subcutaneous sclerosis, ulceration, hyperkeratosis. These skin changes have been known since the early days of medical use of x-rays and radium. Originally they could almost invariably be traced to faulty technic, inadequate protection, or to occupational exposure. The great advance in knowledge of radiation physics and biology and the subsequent development of modern technic have provided means of proper protection, but skin reactions persist, necessitating a new approach from both a medical and legal standpoint. From the legal point of view, the post-irradiation skin reaction should be regarded properly as an unavoidable and unpredictable aftermath of the therapeutic method, unless evidence of negligence or gross lack of knowledge on the part of the practitioner can be shown to exist. From the medical standpoint, skin reactions occurring immediately after radiation treatment heal spontaneously, as a rule, in four to six weeks after completion of exposure, whereas delayed skin reactions, occurring after about six months or later, may not regress spontaneously and therefore demand attention. Atrophy of the skin and telangiectasia do not require treatment, except for cosmetic reasons. Ulceration and hyperkeratosis must have immediate and special care.