The cases of two young men with the Gorham-Stout's syndrome of massive angiomatous osteolysis are presented. Attempted surgical removal of the pathological angiomatous tissue proved unsuccessful. Telegammatherapy with each patient receiving total focal dose of 40.0 Gy fractionated over a period of 4 weeks resulted in speedy and complete arrest of osteolysis, and in partial recalcification of the bone tissue destroyed. In one patient the favourable condition has been lasting for 9 years, in the other for 8 months from the end of the course of radiotherapy. The authors discuss the cause of a central fracture of the first patient's left acetabulum which was noted 5 years after the radiotherapy. Proceeding from their experience so far, the authors describe radiotherapy in the Gorham-Stout's syndrome as a method of choice, and give a list of the therapeutical principles.