While polyandry is essentially ubiquitous across the animal kingdom, the net fitness consequences of multiple mating remain the subject of much debate. In some taxa the costs of multiple mating outweigh potential benefits, and large direct costs are unlikely to be compensated for by indirect benefits. Nevertheless, direct and indirect benefits potentially provide females with substantial fitness returns, and these are manifest in some species. We investigated some fitness costs and benefits of multiple mating in the fly Drosophila simulans. We compared the longevity and lifetime reproductive success of females with intermittent or continual exposure to males with those of singly mated females housed alone or housed with virgin females. We also compared the same fitness components in females mated once, twice and three times. We found no difference in the lifetime reproductive success of females housed intermittently with males and those housed continually with males, but females in these treatments produced more offspring than singly mated females (housed alone or with virgin females). However, females that were continually exposed to males died younger than females from any other treatment. We also found that females who mated more than once had higher lifetime reproductive success, and that number of matings had no influence on residual longevity. These results contrast somewhat with findings from Drosophila melanogaster, and suggest that while polyandry is beneficial for female D. simulans, male harassment can be costly.