Background: Because risk perceptions can affect protective behavior and protective behavior can affect risk perceptions, the relations between these 2 constructs are complex and incorrect tests often lead to invalid conclusions.Purpose: To discuss and carry out appropriate tests of 3 easily confused hypotheses: (a) the behavior motivation hypothesis (perceptions of personal risk cause people to take protective action), (b) the risk reappraisal hypothesis (when people take actions thought to be effective, they lower their risk perceptions), and (c) the accuracy hypothesis (risk perceptions accurately reflect risk behavior).Methods: Longitudinal study with an initial interview just after the Lyme disease vaccine was made publicly available and a follow-up interview 18 months later. Random sample of adult homeowners (N = 745) in 3 northeastern U.S. counties with high Lyme disease incidence. Lyme disease vaccination behavior and risk perception were assessed.Results: All 3 hypotheses were supported. Participants with higher initial risk perceptions were much more likely than those with lower risk perceptions to get vaccinated against Lyme disease (OR = 5.81, 95% CI 2.63-12.82, p < .001). Being vaccinated led to a reduction in risk perceptions, χ2(1, N = 745) = 30.90, p < .001, and people vaccinated correctly believed that their risk of future infection was lower than that of people not vaccinated (OR = .44, 95% CI .21-.91, p < .05).Conclusions: The behavior motivation hypothesis was supported in this longitudinal study, but the opposite conclusion (i.e., that higher risk led to less protective behavior) would have been drawn from an incorrect test based only on cross-sectional data. Health researchers should take care in formulating and testing risk-perception-behavior hypotheses.