During the past decades, the major impact of DNA damage on cancer as 'disease of the genes' has become abundantly apparent. In addition to cancer, recent years have also uncovered a very strong association of DNA damage with many features of (premature) aging. The notion that DNA repair systems protect not only against cancer but also equally against to fast aging has become evident from a systematic, integral analysis of a variety of mouse mutants carrying defects in e.g. transcription-coupled repair with or without an additional impairment of global genome nucleotide excision repair and the corresponding segmental premature aging syndromes in human. A striking correlation between the degree of the DNA repair deficiency and the acceleration of specific progeroid symptoms has been discovered for those repair systems that primarily protect from the cytotoxic and cytostatic effects of DNA damage. These observations are explained from the perspective of nucleotide excision repair mouse mutant and human syndromes. However, similar principles likely apply to other DNA repair pathways including interstrand crosslink repair and double strand break repair and genome maintenance systems in general, supporting the notion that DNA damage constitutes an important intermediate in the process of aging.