IT has often been suggested that sexual selection may have important consequences for life-history evolution and vice versa(1-5). We manipulated the parental effort of male collared flycatchers (Ficedula albicollis) by changing the number of offspring in their nests and found a trade-off between parental effort and the size of the male’s forehead patch (a secondary sexual character) in the following year. We report here that, in addition to this intra-generational trade-off, we found an inter-generational trade-off : the size of the forehead patch in first-year males was negatively related to the change in brood size of the nest in which they were raised. This has consequences for reproductive success because males with large patches mate with more females and have higher lifetime reproductive success. To our knowledge, this is the first experimental demonstration that life-history traits and secondary sexual characters trade off against each other. Our results support the suggestion that the life-history consequences of sexual ornaments are important in their evolution(2-4).