This study analyzes effects of changes in risk perceptions of smoking's health harms on actual and attempted quits and quitting intentions of male smokers in China. Our survey of 5000+ male smokers was conducted two years after their neighbor's lung cancer diagnosis. We use proximity to a lung cancer neighbor as an exogenous determinant of individual's smoking risk perception. We show that learning of a neighbor's lung cancer diagnosis substantially affects smokers' subjective beliefs about smoking's harms, which in turn affects decisions about continued smoking and intentions to quit. Our study findings offer important public policy implications in indicating the importance of designing health-warning messages that fit smokers' personal circumstances as opposed to warnings solely based on edicts from scientific experts and/or epidemiological evidence.