Trade-offs between the expression of sexual signals and the maintenance of somatic and germline tissues are expected when these depend upon the same resources. Despite the importance of sperm DNA integrity, its trade-off with sexual signalling has rarely been explored. We experimentally tested the trade-off between carotenoid-based sexual colouration and oxidative DNA damage in skeletal muscle, testis and sperm by manipulating reproductive schedule (early vs. late onset of breeding) in male three-spined sticklebacks. Oxidative DNA damage was measured as the amount of 8-hydroxy-2-deoxy-Guanosine in genomic DNA. Irrespective of the experimentally manipulated reproductive schedule, individuals investing more in red colouration showed higher levels of oxidative DNA damage in muscle, testis and sperm during the peak breeding season. Our results show that the expression of red colouration traded off against the level of oxidative DNA damage possibly due to the competing functions of carotenoids as colorants and antioxidants. Thus, female sticklebacks may risk fertility and viability of offspring by choosing redder, more deteriorated partners with decreased sperm DNA integrity. The evolution of sexual signal may be constrained by oxidative DNA damage in the soma and germline.