The changes of reproductive functions, fertility and genetic risks of ageing females have been investigated relatively intensively. The state of knowledge about endocrine and reproductive changes in ageing men as well as possible age-related paternal genetic risks lags far behind. In general serum testosterone levels decrease with increasing age. In ageing men testis morphology and semen production can be absolutely normal. However, in some testes degenerative forms of germ cells can be observed. Fertility may be maintained up to a very high age. The genetic quality of sperm produced by older men may be reduced for several reasons, among which age-related increases in germ cell mutations, impairment of DNA-repair mechanisms and apoptotic processes are the most likely. The incidence of several autosomal dominant diseases, such as achondroplasia, polyposis coli, Marfan syndrome, Apert syndrome or basal cell naevi is associated with advanced paternal age, whereas there is no clear evidence for a paternal effect on structural or numeric chromosome anomalies. Hence even if offspring of older men have a slightly increased incidence of certain genetic diseases, the individual risk of such a new disease must be considered as extremely small, as the incidence of these diseases is very low.