We combined the health belief model with the theory of subjective expected utility to derive hypotheses about the relations among health beliefs and preventive decisions. The central implication of this combination of theories is the importance of conceptualizing, measuring, and communicating about health threats in ways that are clearly conditional on action. It is important to distinguish, for example, between how susceptible to a disease a person thinks he or she would be if that person were and were not to take a preventive action. An experimental study of judgments about a hypothetical preventive action was conducted to test many of the theoretically derived hypotheses. A correlation study of dental flossing behavior was conducted to test the hypotheses as they apply to overt behavior rather than to judgment. Results of both studies supported most of the tested hypotheses, especially those related to the conditional conceptualization of health threats. Implications for theory, research methods, and practical applications are discussed.