Background: Some believe that vaccinating young women against human papillomavirus (HPV) will increase their risky behavior. In more formal terms, vaccination lowers risk perception, and people compensate for their lower perceived risk by reducing other preventive behaviors.Purpose: We test several predictions from the risk compensation hypothesis in the context of vaccination behavior.Methods: We obtained a random sample of adults (N=705), interviewing them by phone just as the Lyme disease vaccine first became available to the public and again 18 months later. Analyses controlled for age, sex, education, and race.Results: Vaccinated respondents were less likely to continue engaging in two of five protective behaviors after vaccination. The frequency of these protective behaviors did not dip below that among the unvaccinated respondents.Conclusions: We found some evidence of regression (protective behaviors dropping, after vaccination, to levels reported by the unvaccinated cohort). However, we did not finddisinhibition (exceeding the risk taking of the unvaccinated cohort), the greater threat to public health. Although we will not know for several years what effect HPV vaccination has on other behaviors, if any, data on other vaccinations can offer critically important information in the interim.