Sixty-eight patients with varying degrees of radiation induced bone damage were studied in detail with respect to the absorbed doses in soft tissue of bone and the time-dose-fractionation treatment schemes employed. The cases were divided into 2 large categories of bone damage. The first category included 52 cases of predominantly irreparable injuries; the second included 16 cases of reparable damage. Average values of the NSD (Nominal Standard Dose) required for irreparable osseous injury ranged from 2,120 rets to 3,200 rets (roentgen equivalent therapeutic) depending on site. The average NSD value for reparable osteopathy was in the range of 1,310 nets. Analysis of iso-effect dose curves indicated varying degrees of dependency on the number of fractions on over-all treatment time for the production of radiation osteitis. Preventive measures such as careful treatment planning, utilization of supervoltage irradiation, and avoidance of trauma and infection are stressed.