One of the major criticisms of stated preference data is hypothetical bias. Using a unique dataset of both stated and actual behavior, we test for hypothetical bias of stated preference survey responses. We consider whether respondents tend to overstate their participatory sporting event behavior ex ante when compared to their actual behavior at different registration fees. We find that stated behavior accurately predicts actual behavior at a middle level of respondent certainty, overpredicts actual behavior at a lower level of certainty, and underpredicts behavior at a higher level of certainty. This result suggests that respondent uncertainty corrections can be used to mitigate hypothetical bias and stated preference data can be used to better understand actual behavior in situations where no data exist.