Using data from the National Longitudinal Survey of Youth 1979 (N = 4,050), we consider the relationship between the timing of family formation and positive changes in health behavior. Theories that predict both positive and negative associations are tested. The findings suggest that both mechanisms operate and that the direction of the association depends on the respondent's race or ethnicity. Whites who marry early are less likely to quit smoking, whereas Whites who marry on time and Blacks and Hispanics who marry at all ages are more likely to quit. The analysis refines the understanding of how family formation shapes changes in health behaviors differentially across the life course, and it underscores the difference in this process for individuals from different racial and ethnic backgrounds.