This study investigated the effect of a smoking health message on smokers’ comparative optimism. Two groups watched an anti-smoking scenario, with one group imagining being part of the scenario. Participants, including controls, completed comparative optimism ratings for four smoking-related illnesses. The intervention had negative consequences with both intervention groups reporting significantly higher comparative optimism versus the control group for all four smoking-related illnesses. It is concluded that media health messages can be powerful tools in changing comparative optimism but are influenced by peoples’ prior perceptions. Health messages need to be systematically assessed to understand prior beliefs of the target audience.