Objective: Fear of cancer recurrence (FCR) is a top concern of breast cancer (BC) survivors and their spouses. FCR often occurs within an interpersonal context, yet there has been little research on relationship processes that may influence FCR in patients and spouses. It was hypothesized that the inhibition of disclosure of cancer-related concerns, thoughts, and feelings because of perceived partner disinterest or avoidance (termed social constraints) would predict greater FCR in BC patients and their spouses both globally and in the context of everyday life. Method: Two studies, 1 cross-sectional (N = 46 couples) and 1 daily diary (21 days; N = 72 couples), were conducted to examine the between-person and within-person associations between social constraints and FCR in early stage BC patients and their spouses. Assessments were conducted about 6 months after BC surgery. Results: Global social constraints predicted greater global FCR in patients and spouses at the cross-sectional level, controlling for anxiety symptoms, relationship quality, and patient age, physical impairment, and BC stage. At the within-person level, results indicated that on days when more social constraints were reported, both partners were more likely to report greater FCR, controlling for momentary negative affect and relationship quality. Conclusions: This study is the first to examine the within-person association between social constraints and FCR. These findings suggest relationship processes, particularly inhibition of disclosure, can uniquely influence the experience of FCR for both BC patients and their spouses, pointing to an important consideration for future research and possible intervention development.