Growing evidence points to systematic linkages in various physiological indices among romantic partners. This physiological synchrony may facilitate intimacy and connectedness in couples. However, synchronous increases in physiological arousal could also hamper the respective partners' health. To shed light on the consequences of physiological synchrony as well as their potential gender specificity, the current study examined associations between everyday cortisol synchrony and levels of and subsequent changes to relationship satisfaction and non-high-density lipoprotein (non-HDL) cholesterol levels over a 3-year period. Older couples (N = 85; age range = 60-87 years) provided saliva samples for cortisol estimation 5 times daily for 7 days. They further reported their relationship satisfaction and provided a blood sample that was analyzed for lipid levels up to three times in 1-year intervals. Data were analyzed using dyadic growth curve models. Among wives, higher cortisol synchrony was associated with stronger increases in relationship satisfaction over time (b = 1.61, p = .011) but also stronger increases in non-HDL cholesterol levels over time (b = 2.02, p = .042). For husbands, higher cortisol synchrony was not significantly associated with levels or changes of relationship satisfaction but with higher non-HDL cholesterol levels at Time 1 (b = 6.54, p = .015). Synchrony may be important for bonding and relationship maintenance. However, being strongly linked to a romantic partner's physiology may also have health costs due to the accumulative burden of repeated elevations in cortisol, possibly affecting husbands and wives in different ways. (PsycInfo Database Record (c) 2021 APA, all rights reserved).