Background: Discrepancies within cancer-affected couples can disrupt security within the dyadic relationship during cancer treatment. This study investigated the patients' and caregivers' distress and associations between the caregivers' perception of the patients' degree of open communication and their distress. Participants and Methods: In a cross-sectional survey, 189 pairs of cancer patients (31% gastrointestinal, 34% lung, 35% urological cancers) and their partners were assessed for distress (QSC-R10), depression and anxiety (PHQ-2/GAD-2). The caregivers also reported their perception of the patients' degree of disclosure regarding cancer-relevant topics (CCAT-F Disclosure subscale), caregiver strain (CSI), and unmet needs (SCNS-P&C). Prevalences of clinically significant distress were calculated. Associations were calculated between the caregivers' and the patients' ratings and between the caregivers' distress and their perception of the patients' degree of disclosure. Results: 33% of the caregivers and 25% of the patients exhibited significant anxiety, with a tendency towards a higher frequency in the caregivers (p = 0.10). The prevalence of depression was lower but equally high in caregivers and patients. The caregivers' perceived non-disclosure by the patients was primarily associated with their anxiety (r = 0.31), disease-specific distress (r = 0.32), and psychological/emotional needs (r = 0.35). Conclusion: The identification of caregivers reporting problems in communicating with patients should be pursued in clinical practice as this might indicate that caregivers are particularly burdened.