This paper covers selected aspects of the acute and long term health effects excluding acute radiation syndrome and carcinogenesis, resulting from exposure to ionizing radiation. The changes addressed in this paper are those witnessed within an organ or whole body rather than at the molecular or even cellular level. They include acute and late health effects. Some of these effects are threshold effects, meaning that the dose must exceed a certain threshold before one sees these effects. Less than the threshold dose results in no observable organ or whole body effect. The severity of the effects correlate directly with the amount of cell damage or cell death that has occurred. 15 refs., 4 figs., 8 tabs.