Researchers have documented the interrelatedness of parent–child and marital relationships during the early parenting years, but little is known about how these two family subsystems are associated once children reach adulthood. The authors of the current study addressed this gap by examining parents' relationships with their adult children and their marital satisfaction using an actor–partner interdependence model. Participants included 197 married other‐sex couples (N = 394 individuals; range: 40–69 years of age) who had a child over age 18 years. A spillover effect was found among fathers, indicating that parent–child relationship quality was positively associated with marital satisfaction, but the same was not found for mothers. Interestingly, a negative crossover effect was also found, meaning that more negative relationship quality between mothers and their adult children was associated with lower marital satisfaction on the part of the father. These findings suggest that the interdependence between parent–child and marital relationships persist once children reach adulthood.