Objective: A diagnosis of breast cancer disrupts the life of the patient, but also the partner may experience adverse psychological effects. We examined partners' risk for first use of antidepressant medication, as a proxy for pharmacologically treated depression. Methods: By linkage of national registers, we identified 1 420 592 depression-free men living with a cancer-free female partner in 1998 to 2011. During follow-up, breast cancer was diagnosed in female partners of 26 256 men. In Poisson regression models, we estimated the rate ratios for first use of antidepressant medication compared to partners of breast cancer-free women. Cox regression analyses examined associations between exposed partners' sociodemographic characteristics, somatic comorbidity, death of female partner, and first use of antidepressant medication. Results: Male partners of women with breast cancer had an increased rate ratio of 1.08 (95% CI, 1.03-1.13) for first use of antidepressant medication compared to the background population, corresponding to excess absolute risk of 12 cases per 10 000 person-years. This increased risk persisted throughout 14 years of follow-up. Higher age, shorter education, somatic comorbidity, and death of female partner were associated with increased risk among men whose partner had breast cancer. Conclusion: The modest, but long term, increased risk for first use of antidepressant medication calls for attention by health care professionals to symptoms of depression among partners of breast cancer patients.