Breast cancer (BC) is the most frequent female carcinoma and the major cause of death in women aged 35--50 years. The total number of patients surviving BC and especially the morbidity rate of patients below the age of 55 years has increased significantly in the last several years. As a consequence, the number of BC patients suffering from the long-term effects of estrogen deficiency due to adjuvant treatment is increasing. At present, hormone replacement therapy (HRT) following BC treatment is applied individually and mainly depends on the severity of postmenopausal symptoms (PMS) experienced by these patients. In a retrospective study (total n = 185 BC patients, 64 with and 121 without HRT), the effect of HRT during or after adjuvant therapy [chemotherapy and/ or (anti-) hormonotherapy] has been investigated. The surveillance period was up to 60 months. Evaluated were HRT effects on (1) PMS measured by a comprehensive life quality questionnaire, (2) bone mineral density (BMD) measured by osteodensitometry and (3) morbidity as well as mortality rates. Both groups did not differ with regard to tumor stage, lymph node involvement, metastasis, grading, and steroid hormone receptor status. A reduction in PMS was significant in women taking HRT (p < 0.001), especially in the subgroup of women < or =50 years (p < 0.0001). For both age groups, the median reduction in BMD (z-score) was less in women receiving HRT (< or =50 years: without HRT -1.99 vs. with HRT -0.95, p < 0.05; >50 years: without HRT -2.29 vs. with HRT -1.19, p < 0.01). There were no statistically significant differences regarding morbidity and mortality (p = 0.29). In this study of BC patients, the use of HRT shows positive effects on PMS and BMD. There was no significant influence on morbidity or mortality. However, a reevaluation of HRT in the routine management of BC patients should await the results of prospective randomized trials. Copyright 2001 S. Karger AG, Basel