Thesis advisor: Summer H. Hawkins / Thesis advisor: David Takeuchi / Dramatic increase in the number of people living to old age has led to a higher prevalence of three-generational households during the last few decades. And co-resident grandparents play a more important role in the lives of children as caregivers in three-generational households. However, little is known about the longitudinal effects of co-resident grandparents on grandchildren’s health. Using the National Longitudinal Study of Adolescent to Adult Health (Add Health) from Wave I-III, this three-paper dissertation explored the longitudinal effects of co-residence with grandparents on the physical and psychological health of grandchildren in three-generational households across racial/ethnic groups. Paper 1 investigated the determinants of co-residence with grandparents in three-generational households within the family context, showing that co-residence with a grandparent was associated with low socio-economic status for white families, and with family culture for Hispanic families. Paper 2 examined the influence of co-residence with grandparents on BMI trajectories as adolescents age into emerging adulthood across racial/ethnic groups. The results showed that Hispanic adolescents who lived with a grandparent showed significantly slower rates of BMI growth compared to those who have not lived with a grandparent during adolescence. Paper 3 examined how co-residence with a grandparent affects adolescents’ depressive trajectories as they age into early adulthood and whether this relationship varies by immigrant generational status. The results showed that Asian first-generation immigrant adolescents experienced less depressive symptoms than Asian second- and third- generation immigrant adolescents in three-generational households. This dissertation suggested that we attempt to provide intergenerational policies and services to improve the well-being of all family members. / Thesis (PhD) — Boston College, 2017. / Submitted to: Boston College. Graduate School of Social Work. / Discipline: Social Work.