This study examined whether perceived risks of heart attack, cancer, and stroke were higher among smokers than nonsmokers; whether smokers were more likely to underestimate these risks; and the demographic correlates of unrealistic risk estimation among smokers. Two thousand seven hundred eight-five patients from 12 North Carolina family practices completed a questionnaire including a health risk appraisal and questions concerning smoking behavior and perceived risks of heart attack, cancer, and stroke. While most smokers accurately perceived their health risks to be greater than nonsmokers', smokers were also more likely to underestimate their risks. This optimistic distortion of risk was associated with age, gender, and education levels. Smokers may not yet understand the magnitude of health risks posed by smoking. These data suggest the need for renewed attention to perceptions of the health risks of smoking. As long as smokers underestimate their risks, they underestimate the imperative to quit.