Depression is common among patients with breast cancer (BC) and their spouses. The diagnosis of BC often results in negative cognitive processes, such as appraisals of harm/loss, intrusive thoughts, and depressive rumination, all of which contribute to the occurrence of depression in both the patient and spouse. The present research is a cross-sectional exploration of the mediating role of depressive rumination in the relationships of intrusive thoughts and appraisal of harm/loss with depression, in a sample of 56 BC patients and their partners. We hypothesized that depressive rumination would mediate the relationships between cognitive processes and depression in both BC patient and their partners. Participants completed self-report measures of depressive symptoms, depressive rumination, cognitive appraisals, and intrusive thoughts. Path analyses using hierarchical linear regression were conducted to assess the relationships among variables. Results indicated that for BC patients, harm/loss appraisals and intrusive thoughts had direct effects on depression; only harm/loss appraisals had indirect effects through depressive rumination. For partners, both harm/loss appraisal and intrusive thoughts had direct effects on depression, and both had indirect effects through depressive rumination. Dyadic analysis showed no relation of partner cognitive variables with patient depression or patient cognitive variables with partner depression. Findings show that the perseverative practice of dwelling on these negative thoughts of loss and harm relates to depressive symptoms. Rumination may act as 1 possible mechanism by which intrusive thoughts and harm/loss appraisals lead to depressive symptoms.