Previous research showed that conscientiousness (social dependability) in childhood predicted longevity in an archival prospective cohort study of bright children first studied by Terman in the 1920s (H. S. Friedman et al., 1993). Possible behavioral mechanisms for this robust association are now examined by gathering cause of death information and by considering the possible mediating influences of drinking alcohol, smoking, and overeating. Survival analyses (N = 1,215) suggest that the protective effect of conscientiousness is not primarily due to accident avoidance and cannot be mostly explained by abstinence from unhealthy substance intake. Conscientiousness may have more wide-ranging effects on health-relevant activities.