Primates exhibit an array of mating behaviours and arrangements, from monogamy to promiscuity, or mate-guarding to multiple-mating. We have previously explored the role of adult sex ratio in determining the likelihood of males choosing either promiscuity or monogamy, but many questions remain open. In particular, do (and, if so, how do) longevity and life history contribute to the choice of male strategy? And how can we characterise the effectiveness of guarding for those males who employ that strategy? We examine some of the trade offs that arise, and how they can influence the choice of male strategy.