We examined young adults' essentialist reasoning about gender categories. Previous developmental results suggest that until age 9 or 10, children show marked essentialist reasoning about gender, but this disappears by early adulthood. In contrast, results from social cognition suggest that essentialist thinking about social categories persists into adulthood. To address this discrepancy, 69 undergraduates engaged in a switched-at-birth task under speeded or delayed conditions. Delayed participants made essentialist decisions about physical but not behavioral properties and replicated past findings. Speeded participants showed markedly higher essentialist responding for behavioral properties compared with delayed participants. These findings suggest that gender essentialism does not necessarily diminish in adulthood but instead may be suppressed by more explicit reasoning processes.