It is unclear if depression or depressive symptoms have an effect on mortality in breast cancer patients. In this population-based, nationwide, retrospective cohort study in Denmark, depression was defined as affective or anxiety disorders that necessitated psychiatric hospital admission. All the affective and anxiety disorders were divided and categorized into five ordinal diagnostic groups. Early-stage (N=10382) and late-stage (N=10211) breast cancer patients were analyzed separately with Cox's regression adjusted for well-documented somatic prognostic variables. The authors used survival analysis of data from three central registers and found that breast cancer patients with depression had a modestly but significantly higher risk of mortality depending on stage of breast cancer and time of depression. The same result was found after censoring unnatural causes of death such as accident, suicide, or homicide.