Seventy-two tumors, mostly in deep locations, were studied retrospectively with computed tomography (CT) before and after thermoradiation therapy. Hyperthermia was administered locally or regionally with radio frequency capacitive heating equipment after irradiation (total dose, 20-70.2 Gy) for 40-60 minutes per session in a total of four to 13 sessions. Sixteen of the 72 tumors showed complete regression. Tumor regression was not related to the average maximum or minimum tumor temperature. CT scans obtained after thermoradiation therapy demonstrated a clear low-density area in 32 of 56 tumors that did not regress completely. Histopathologic examinations, performed in 14 of the 32 tumors, showed the low-density area to be massive coagulation necrosis. The low-density area was classified into three types according to its percentage area in the tumor: type 3 (more than 80%), type 2 (50%-80%), and type 1 (less than 50%). The type correlated with the average maximum and minimum tumor temperature, and follow-up observations and histopathologic examinations showed great effects in most of the type 3 tumors.