The authors studied the factors which favour necrosis after curietherapy, in a series of 82 patients with epithelioma of the oral cavity and a previous series of 280 cases. The principal factor is the size of the tumor. The other factors (macroscopic appearance, dose, quantity of radioactive material, degree of inhomogeneity, distance between the lines, association with external irradiation), are or only moderate importance, as shown by the variations observed, though they are difficult to evaluate in an exact manner, partly for methodological reasons. The frequency of necrosis of bone tissue is directly relaxed to the number of radioactive lines in contact with the maxilla. Alcohol and tabacco abuse have a definite influence but this cannot be calculated. In conclusion, therefore, it would appear possible to reduce the frequency of necrotic lesions by reducing the tumoral size by curietherapy, by applying no more than 2 lines in contact with the mandible for bony necrotic lesions, and by stopping the abuse of alcohol and tobacco.