Entrepreneurs are more susceptible to certain cognitive biases than are managers who are not entrepreneurs, but it is not clear why. In an effort to help explain why, I examine differences in the degree to which entrepreneurs exhibit the overconfidence bias. Results show that individual age, firm decision comprehensiveness and external equity funding affect the degree to which entrepreneurs are overconfident. In addition, founder-managers are shown to be more overconfident than are new-venture managers who did not found their firms. The results suggest that entrepreneurs' cognitive biases are a function of both individual and contextual factors.