Evolutionary selection pressures have been one of the factors proposed to underlie sex differences in inhibitory control. Consequently, inhibitory control may vary as a function of the menstrual cycle and may be modulated by the stimuli being processed if these stimuli are related to reproductive success. We used functional MRI to study women's brain activation across the menstrual cycle on a GO/NOGO response inhibition task using attractive male and female faces as stimuli. We detected brain activity changes for both successful inhibitions and errors of commission that were unique to the male stimuli during the follicular phase of the menstrual cycle. That is, when pregnancy was possible women had superior inhibitory brain function and heightened detection of inhibitory failures when processing male stimuli. Moreover, we show that individual differences between females in sexual desire and social risk taking negatively correlate with error-related brain activity to the male stimuli during the follicular phase of the menstrual cycle. These results suggest an interaction between hormonal influences and stimulus-specific effects in producing an endophenotypic outcome predicted by evolutionary psychology, and suggest that the functioning of the brain's monitoring system can predict individual differences in both traits and real-world risk-taking behaviours.