OBJECTIVES: High rates of compliance and persistence to medical treatments are associated with improved patient outcomes. Breast cancer survival has significantly increased, compliance with adjuvant treatment is very importance to ensure optimal treatment outcome. In this analysis, persistence i.e. the extent to which patients continue treatments was estimated for breast cancer patients on tamoxifen (TAM) and aromatase inhibitors (AI) treatment in primary care practices in Germany. METHODS: This retrospective cohort study analysed longitudinal routine care data collected by gynaecologists and general practitioners in Germany (IMS® Disease Analyzer). Non-persistence was defined as a period of ≥180 days without prescriptions. The lack of persistence was compared using Cox regression models after adjusting for age, gynecologist care, private health insurance, urban residency, practice in West-Germany, defined co-diagnoses and co-therapies (i.e. bisphosphonates). RESULTS: We included 12,412 patients diagnosed with primary breast cancer and first-time prescriptions of hormone therapy. A total of 7312 patients started with TAM (mean age 62.1 (SD: 13.5)), 5,100 with AI (anastrozole, exemestane, letrozole) (mean age 66.4 (SD: 10.6) as first line treatment. After 3 years 42.1% of TAM-patients and 40.2% of AI-patients in German practices discontinued their treatment. In the adjusted Cox model treatment in gynaecologist practice (HR: 0.46, p<0.001), age over 70 (HR 0.90, p=0.010), change of hormone therapy substance (HR: 0.82, p<0.001), co-therapy with bisphosphonates (HR: 0.86, p=0.013) and diagnosis of diabetes mellitus (HR: 0.82, p<0.001) were associated with a lower risk of discontinuation of therapy. No significant effect was found for western Germany, urban residency, private insurance status and other age groups. CONCLUSIONS: Long-term persistence on hormonal treatment in women with endocrine-responsive breast cancer is low. Factors affecting treatment discontinuation need to be identified and properly addressed. Patients at high risk of non-adherence to the prescribed medication should be cared for in more individualised fashion to ensure optimal treatment outcome.