The lack of obvious visible manifestations of ovulation in human females, compared with the prominent sexual swellings of many primates, has led to the idea that human ovulation is concealed. While human ovulation is clearly not advertised to the same extent as in some other species, we show here that both men and women judge photographs of women's faces that were taken in the fertile window of the menstrual cycle as more attractive than photographs taken during the luteal phase. This indicates the existence of visible cues to ovulation in the human face, and is consistent with similar cyclical changes observed for preferences of female body odour. This heightened allure could be an adaptive mechanism for raising a female's relative value in the mating market at the time in the cycle when the probability of conception is at its highest.