Objective: Comparatively little longitudinal data exist focusing on grandparent caregiving, to say nothing of health’s impact over time on grandparent and grandchild well-being. Accordingly, the present study explored relationships among grandparent caregiver physical health, well-being, and adjustment, as well as with grandchild well-being across a 1-year period. Method: Participants were 79 grandparents who had full-time responsibility for their grandchildren. Measures of grandparent physical health, well-being, and grandchild well-being were completed across two assessments, 1 year apart. Results: Cross-lagged analyses exploring potential causality over time suggested that with one exception, the relationships between health and well-being appeared to be bidirectional. Discussion: In general, these longitudinal data indicate that better perceived health may provide an adaptive advantage for both grandparent caregivers and their grandchildren, yet also underscore to the potentially causal role that proactivity in the face of adversity plays in the maintenance and improvement of grandparent caregiver health over time.