OBJECTIVES: This cost-utility analysis evaluated the cost-effectiveness of primary endocrine therapy (PET) comparing against  surgery as the initial treatment strategy in older women with primary breast cancer. METHODS: The analysis was conducted from the United Kingdom (UK) National Health Service perspective for a 5-year time horizon. Clinical effectiveness (life years gained; LYG) and costs (in British pounds of year 2014) of treatment pathways were assessed using a longitudinal database collected in a regional hospital. The database followed clinical outcomes of 1759 older women (age≥70 years) with primary breast cancer up to 37 years. Utilities were predicted using a previously published mapping algorithm to calculate quality-adjusted life-year (QALY). The base-case analysis included patients who were treated by either surgery or PET in the database. Patients treated with surgery were matched (2:1) to patients treated with PET by propensity score estimated from their baseline covariates. Incremental cost-utility ratios (ICURs) were calculated to derive cost-effectiveness plan and cost-effectiveness acceptability curve. Mean ICURs for the base-case cohort and a subgroup of patients with higher oestrogen receptor content (H-score>250 out of 300) were also calculated by probabilistic sensitivity analysis. RESULTS: Overall, 1684 patients were included in the base-case analysis. Comparing with surgery, PET was associated with lower costs and QALYs, and the mean ICUR was £2175.15 (95%CI: -10,278, 10,790) per QALY. Likewise, for patients with H-score>250, PET was associated with lower costs and QALYs, the mean ICUR was £4001,07 (95%CI: -18,690, 19,025) per QALY. CONCLUSIONS: The PET was a chapter but less cost-effective initial treatment strategy than surgery for older women with primary breast cancer based on the effectiveness data collected from a single centre. The lack of frailty and comorbidity data may confound the incremental effectiveness results, and further large-scale and prospective studies are needed to confirm the cost-effectiveness of PET.