Many studies investigate the benefits of polyandry, but repeated interactions with males can lower female reproductive success. Interacting with males might even decrease offspring performance if it reduces a female’s ability to transfer maternal resources. Male presence can be detrimental for females in two ways: by forcing females to mate at a higher rate, and through costs associated with resisting male mating attempts. Teasing apart the relative costs of elevated mating rates from those of greater male harassment is critical to understand the evolution of mating strategies. Furthermore, it is important to test if a male’s phenotype, notably body size, has differential effects on female reproductive success versus the performance of offspring, and whether this is due to male body size affecting the costs of harassment or the actual mating rate. In the eastern mosquitofish Gambusia holbrooki males vary greatly in body size, and continually attempt to inseminate females. We experimentally manipulated male presence (i.e., harassment), male body size, and whether males could copulate. Exposure to males had strong detrimental effects on female reproductive output, growth and immune response, independent of male size or whether males could copulate. In contrast, there was little evidence of a cross-generational effect of male harassment or mating rate on offspring performance. Our results suggest that females housed with males pay direct costs due to reduced condition and offspring production, and that these costs are not a consequence of increased mating rates. Furthermore, exposure to males does not affect offspring reproductive traits.