We evaluated factors associated with use of antidepressant medication subsequent to a diagnosis of breast cancer. We also evaluated the effect of participation in a cancer rehabilitation program on use of antidepressants. Material and methods. We conducted a register-based cohort study of 1 247 women with breast cancer diagnosed between 1998 and 2006 who attended a week-long rehabilitation program and a comparison group of 2 903 women who did not attend the program matched through the registers of the Danish Breast Cancer Cooperative Group. The associations between breast cancer-related, treatment-related, and sociodemographic factors and use of antidepressants were evaluated in multivariate Cox proportional hazard models separated on use of antidepressants before diagnosis of breast cancer. Results. The mean follow-up for the 4 150 women in the study was 3.3 years (595% range, 0.37.0 years) and 1 020 (25%) were users of antidepressants after diagnosis of breast cancer. Among women who had not used antidepressants before their breast cancer, the diagnosis of a new primary cancer increased the adjusted hazard ratio (HR) to 3.34 (95% CI, 1.507.76), and recurrence of breast cancer increased the HR for first use of antidepressants to 2.56 (95% CI, 1.863.52). Unemployment was associated significantly with use of antidepressants, whereas having no children living at home, lower income, and the number of tumor-positive axillary lymph nodes were of borderline significance. No effect of the rehabilitation program was observed on first use of antidepressants after breast cancer. Discussion. Diagnosis of a new cancer or recurrence of breast cancer considerably increased the rate of use of antidepressants. Sociodemographic rather than disease- or treatment-related characteristics at the time of diagnosis were associated with first use of antidepressants after a breast cancer diagnosis.