The effects of mutations induced by ionizing radiation on human health can be subdivided into decrease of general viability, malformations and embryonic death. Reasons are given for the recommendation why a man whose gonads had been exposed to radiation should refrain from procreation for a couple of months. An analysis of the frequency of chromosome aberrations induced in lymphocytes can provide an estimate of the dose received during an accidental exposure. Radiation induced chronic myeloid leukaemia is probably based on the induction of an aberration involving chromosome 22 in a bone marrow cell (deletion, translocation). The relationship between the frequency of radiation induced point mutations and the DNA content of the genome of the species studied so far is discussed.