Recent research shows that women experience nonconscious shifts across different phases of the monthly ovulatory cycle. For example, women at peak fertility (near ovulation) are attracted to different kinds of men and show increased desire to attend social gatherings. Building on the evolutionary logic behind such effects, we examined how, why, and when hormonal fluctuations associated with ovulation influenced women's product choices. In three experiments, we show that at peak fertility women nonconsciously choose products that enhance appearance (e.g., choosing sexy rather than more conservative clothing). This hormonally regulated effect appears to be driven by a desire to outdo attractive rival women. Consequently, minimizing the salience of attractive women who are potential rivals suppresses the ovulatory effect on product choice. This research provides some of the first evidence of how, why, and when consumer behavior is influenced by hormonal factors.