This study examined how variation in a critical environmental variable, protein content in the adult diet, influenced male mating signals, mating success and male ‘quality’ in a lekking Hawaiian Drosophila, D. grimshawi . Specifically, the effects of low- and high-protein-containing diets on male physical condition, courtship behaviour, copulation success and adult offspring production were investigated. Potential differences in attractiveness to females were investigated by recording times to mating. Males fed high-protein diets were in better physical condition, courted more vigorously, and mated more often and sooner than males fed low-protein diets. Matings involving males fed a high-protein diet resulted in more eclosing offspring than matings involving low-protein-fed males. Because females control when mating occurs in this species, these results indicate that females may have preferred males fed high-protein diets. The results are discussed in light of recent questions regarding female choice and the possible benefits that females of lekking species might gain by discriminating between males.