Background Fear of a breast cancer recurrence is the most prevalent and disruptive source of distress for long‐term survivors and their partners. However, few studies have focused on predictors of fear of recurrence. The aim of this study is to test the efficacy of the Social Cognitive Processing Theory (SCPT) in predicting fear of recurrence in long‐term breast cancer survivors diagnosed at age 45 years or younger and their partners. Methods In a large cross‐sectional study, breast cancer survivors (n = 222) 3–8 years from diagnosis and their partners completed a survey assessing demographic characteristics, fear of recurrence, social constraints, and cognitive processing (intrusive thoughts and cognitive avoidance). Mediation analyses were conducted for survivors and partners separately to determine if cognitive processing would mediate the relationship between social constraints and fear of recurrence. Results Cognitive processing mediated the relationship between social constraints and fear of recurrence both for survivors [F(3,213) = 47.541, R2 = 0.401, p < 0.001] and partners [F(3,215) = 27.917, R2 = 0.280, p < 0.001). Demographic variables were not significant predictors of fear of recurrence. Conclusions As predicted, cognitive processing mediated the relationship between social constraints and fear of recurrence. Results expand the utility of the SCPT in long‐term survivors and their partners by supporting its use in intervention design. Copyright © 2015 John Wiley & Sons, Ltd.