Secondary sexual characteristics may indicate quality of the immune system and therefore a preference for masculinity may confer genetic benefits to offspring; however, high masculinity may be associated with costs of decreased paternal investment. The current study examined women's preferences for masculinity in male faces by using computer graphics to allow transformation between feminine and masculine versions of individual male faces. We found that preferences for masculinity are increased when women either have a partner or are considering a short–term relationship. Such preferences are potentially adaptive, serving to: (i) maximize parental investment and cooperation in long–term relationships by biasing choices towards feminine faced males, and (ii) maximize possible good–gene benefits of short–term or extra–pair partners by biasing choices towards masculine faced males. We also found that individuals using oral contraception do not show the above effects, indicating that such hormonal intervention potentially disrupts women's choices for evolutionarily relevant benefits from males.