In this study, based on Family Interactional Theory (FIT), the authors tested a longitudinal model of the intergenerational effects of the grandmothers' parent-child relationships and the grandparents' smoking on the grandchildren's externalizing behavior via parents' psychological symptoms, tobacco use, and child rearing. Using Mplus, the authors obtained a structural equation model that demonstrated generational associations from grandmothers (G1) to parents (G2) to their oldest children (G3) and thus was in accord with FIT. They identified a pathway from the grandmothers' parenting to the grandchildren's externalizing behavior via the parents' psychological symptoms, their smoking, and their child rearing. Parents' psychological symptoms in adolescence were associated with their tobacco use in their late twenties, controlling for the continuity of their psychological symptoms and their tobacco use. This 3-generational model adds to the literature on parent-child relationships (G1), smoking from adolescence to early adulthood (G2), and externalizing behavior in the G3 child. (Contains 2 tables, 1 figure, and 1 note.)