Experimental data from the literature are presented to create a chain which links radiation induced cancer in animals to cell reproductive death and then to chromosomal aberrations and somatic mutations. The cancer data reveal the same peak value of cancer induction following different radiation exposures which leads to an association between cancer induction and cell killing. Other data show a direct correlation between cell survival and chromosomal aberration yield independent of whether a sensitiser is used or not. Data on the induction of somatic mutations in mammalian cultured cells show the same direct relationship between mutation frequency and cell killing following neutron and gamma ray exposures. Taken as a whole, the experimental data provide convincing evidence that radiation induced cancer arises from chromosomal damage.