Correlations between risk perceptions and risk behaviors are used by investigators to answer 2 important and easily confused questions: Are individuals' perceptions of their personal risk accurate, correctly reflecting their precautions and their risk-increasing behaviors? and Does recognition of high personal risk cause people to adopt precautions to reduce that risk? Researchers who use survey data to investigate these questions often look at the wrong correlations to get their answers. Furthermore, as members of a population adopt precautions and change their risk status, correlations between perceived risk and risk behavior in this population also change. A mathematical model of precaution adoption--allowing a bidirectional relationship between perception and behavior--is used to illustrate the different correlations between risk perception and risk behavior that can be examined and the changes in correlations that can occur with the passage of time. Recommendations are provided concerning the correlations most appropriate for answering each of the 2 preceding questions. Which correlation is appropriate to answer the second question varies depending on whether a study is begun before people have taken precautions or after ample time to take precautions has already passed.