Radiation treatment of the liver for malignant disease has gained renewed interest due to newly developed treatment modalities. Still limited specific knowledge is available concerning liver damage following irradiation. Inconsistencies between reported animal experimental studies are largely due to differences in irradiation techniques and to varying observation periods. Following the introduction of Megavoltage irradiation and the development of more sophisticated irradiation techniques, clinical reports concerning more reliable studies became available. The reaction of the liver to irradiation depends specifically on parameters as type of irradiation, dose, dose rate, fractionation schedule, and irradiated volume. Also the use of cytotoxic agents and liver surgery are of importance for the ultimate therapeutic result. Radiation hepatitis in humans may develop following high-dose liver irradiation resulting in clinical and histopathological disorders resembling a veno-occlusive disease-like syndrome. These disorders may either totally or partially recover or be progressive in time resulting in hepatic failure. It is concluded that depending on the variables mentioned, ionizing radiation up to 35 Gy to the human liver, given to a limited volume, can be applied without major liver function disturbances.