Couples managing chronic illnesses-the leading causes of death and disability in the United States-can experience challenges in their daily lives and relationships. Both couple members have reported lower satisfaction, greater burden, and communication difficulties. Many of these illnesses are nonvisible or concealable, increasing fear and uncertainty when sharing illness information, and reducing self-disclosure. These challenges can leave couples vulnerable to dissatisfaction and distress. In this longitudinal study, we integrated dyadic coping frameworks to examine how couples' communication and coping predicted relational well-being over time. Couples, where one partner was diagnosed with a concealable chronic illness, completed three online surveys 6 months apart (n = 242 couples at baseline, 146 couples at 6 months, and 123 couples at 12 months). Couples were recruited from university settings. Actor-partner interdependence mediation models using within-person multilevel dyadic path modeling tested the theoretical model. For patient and partner actor effects, at times when they saw the illness as shared and something that they could manage together, the more they talked about the illness and used dyadic coping strategies (p < .001). In turn, when using dyadic coping strategies more often, patients and partners felt more satisfied, close, and sexually satisfied than they typically felt that year (p < .001). For cross-partner effects, when patients talked about the illness more than usual, their partners also used dyadic coping strategies more often (p = .01). Patients' open communication may not only benefit themselves but also their partners. This multifaceted approach offers new insight into promoting relational well-being while managing concealable chronic illness. (PsycInfo Database Record (c) 2024 APA, all rights reserved).