The mechanisms of post radiation life span alteration are reviewed and discussed. The mechanisms underlying radiation induced organism aging and death are not well understood and under great interest. What is the cause of radiation-induced "aging"? What are the mechanisms leading to senescence and death? Recent achievements in molecular biology and genetics suggest that cell senescence is determined by telomeres reduction (Biokhimiya, 1997). This mechanism seems to play an important role in aging. However the aging in postmitotic organisms (for example Drosophila melanogaster) can not be explained by telomeres reduction mechanism. It is suggested that radiation induced life span alteration can be explained by deregulation of apoptosis in multicellular organisms.