INTRODUCTION: Premenopausal women with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) metastatic breast cancer (mBC) have complex treatment needs and may receive sequential combinations of endocrine therapy (ET) or chemotherapy. This study describes healthcare utilization (HRU) and costs among premenopausal women with HR+/HER2- mBC in real-world settings from a payer's perspective. METHODS: In this retrospective cohort study, premenopausal women with HR+/HER2- mBC who received ET or chemotherapy were identified from the Truven Health Analytics MarketScan database (1 January 2006-31 December 2015). The main HRU outcomes per patient per 6 months (PPP6 M) were measured during each line of therapy and included number of days in inpatient (IP) and outpatient (OP) services. Healthcare costs per patient per month (PPPM) included medical and pharmacy costs. RESULTS: A total of 3203 patients received first-line, 2194 received second-line, and 1242 received third-line therapy for mBC. Mean number of IP days PPP6 M were 1.6, 1.3, and 1.5 days in the first, second, and third lines, respectively. Mean number of days with OP services PPP6 M was 31.4, 30.9, and 23.3 in the first, second, and third lines, respectively. Among patients receiving ET, mean total healthcare costs were $6521, $4440, and $4555 PPPM in the first, second, and third line, respectively. Among patients receiving chemotherapy, mean total healthcare costs were $16,842, $12,868, and $16,129 PPPM in the first, second, and third line, respectively. These costs were mainly driven by treatment and OP costs. CONCLUSION: Real-world HRU and costs among premenopausal women with HR+/HER2- mBC are extensive. Patients who received chemotherapy incurred approximately twice the costs of patients treated with ET. FUNDING: Novartis Pharmaceutical Corp.