While early radiation lesions might be a direct consequence of parenchymal cell loss, late‐radiation injury most probably develops as a consequence of functional perturbations that may involve both parenchymal and nonparenchymal elements. Damage to blood vessels and consequent perturbations in blood flow and endothelial physiology play an important role in the development of late effects. The development of late‐radiation damage has been studied in three different tissue systems: the skin, kidney and central nervous system. The results suggested that damage to vascular tissue played a major role in the development of radiation‐induced late effects.