Fear appeals can lose their persuasiveness when they elicit defensive reactions. For instance, smokers might personally underestimate the health risks presented in the fear appeals. Thus, they might underestimate smoking related health risks for themselves compared to the health risk they perceive for other smokers, which is called unrealistic optimism. When smokers are optimistically biased in terms of their health consequences of smoking, they will hardly quit. For this reason, the national tobacco prevention campaign SmokeFree 2015-2017 addressed this optimistic bias in a TV-spot (target spot). A representative sample of 724 smokers participated in a longitudinal study with two waves. As expected, smokers decreased unrealistic optimism when they had seen the target spot. A wear-in/wear-out effect was found, that is an inverted U-shaped relationship between exposition of the target spot and the reduction of smokers' unrealistic optimism. As assumed, intention to quit smoking increased, the more unrealistic optimism was reduced. Other campaign content had no effect on reducing unrealistic optimism of smokers, even though health risks of smoking were mentioned as well. These results imply that addressing unrealistic optimism in an antismoking campaign may decrease smokers' unrealistic optimism, and this way intention to quit smoking will increase. Implications for tobacco prevention and for future research are discussed.