Men are entering the later stages of life at an unprecedented rate. As fathers and their children age, a gradual transition in the hierarchy of their relationship occurs, eventually resulting in fathers being recipients, rather than providers, of care. Unfortunately, little is known about the effect that adult children (children ages 19 years old and above) have on fathers’ physical and mental health in the middle-to-late stages of life. Using a sample of 588 fathers who were between the ages of 50- and 80-years-old and who had at least one adult child, a series of structural equation models using a cross-lagged panel design were conducted to increase our understanding of 1) the nature of the associations among fathers’ physical health, mental health, relationship quality with their spouse, and relationship quality with their adult children over time in middle-to-late adulthood, and 2) how these associations change as fathers age in middle-to-late adulthood. The findings indicate that fathers’ mental health is strongly correlated with their physical health, marital relationship quality, and relationship quality with their focal child across all age groups of fathers between 57- and 80-years-old. However, a transition seems to occur for fathers between 63- and 68-years-old that increases the within-time salience of fathers’ relationship quality with their focal child. In spite of the strong bivariate correlations, the structural equation models revealed high levels of within-trait stability and a lack of cross-trait predictive power among each of these aspects of fathers’ lives across age groups. The lone exception to this was in the emergence of a significant effect from father’s mental health between the ages of 69- and 74-years-old to their father-child relationship quality six years later, suggesting the possibility of a final transition in father-child relationship dynamics late in fathers’ lives.