Background: A few small studies published to date have suggested that major psychosocial problems develop in the partners of cancer patients; however, to the authors' knowledge, no studies to date have addressed their risk for severe depression. In a retrospective cohort study, the risk for hospitalization with an affective disorder of the male partners of women with breast cancer was investigated, using unbiased, nationwide, population-based information. Methods: Followed were 1,162,596 men born between 1925 and 1973 who were aged ≥30 years at study entry, resided in Denmark between 1994 and 2006, had no history of hospitalization for an affective disorder, and had lived continuously with the same partner for at least 5 years. A Cox regression analysis included detailed clinical information regarding the diagnosis and treatment of breast cancer and on annually updated socioeconomic and health-related indicators obtained from national administrative and disease registers. Results: During the 13 years of follow-up, breast cancer was diagnosed in the partners of 20,538 men. On multivariable analysis, men whose partner was diagnosed with breast cancer were found to be at an increased risk of being hospitalized with an affective disorder (hazards ratio, 1.39; 95%confidence interval, 1.20-1.61), with a dose-response pattern for the severity of breast cancer. Furthermore, men whose partner died after breast cancer had a significant, 3.6-fold increase in risk for an affective disorder when compared with men whose partner survived breast cancer. Conclusions: The results of the current study supported the hypothesis that men whose partner had breast cancer were at an increased risk for hospitalization with an affective disorder. Cancer 2010. © 2010 American Cancer Society. This cohort study supported the hypothesis that the male partners of women with breast cancer are at a significantly increased risk for hospitalization with affective disorders. Results concluded that a diagnosis of breast cancer not only affects the life of the patient but may also seriously affect their partner.