INTRODUCTION: Postmenopausal osteoporosis (PMO) increases the risk of fragility fractures (FF), leading to disability, higher mortality, and elevated healthcare costs. Despite available treatments, osteoporosis (OP) remains undertreated, especially in women over 50 years at high risk for FF. Real-world data on OP care in Spain are limited. This study aims to assess the OP treatment gap, healthcare resource utilisation (HCRU), and costs among Spanish women following a first FF or PMO diagnosis. METHODS: This retrospective study used data from the BIG-PAC RESULTS: The study included 22,142 women: 3190 in cohort 1 and 18,952 in cohort 2. The OP treatment gap was higher in cohort 1 vs cohort 2 (41.5% vs 23.6%). In cohort 1, 59.2% were diagnosed with PMO after the first FF, with 88% experiencing subsequent fracture(s). OP treatment persistence decreased over time in both cohorts. Fracture rates were lower in women prescribed OP treatment vs those who were not (8.35 vs 13.8 per 1000 patient-years) and in those who showed 24-month-persistence and 12-month adherence to treatment vs those who did not (8.98 and 7.66 vs 10.79 and 10.76). The 2-year mean cost per patient was higher in cohort 1 (€10,601) than in cohort 2 (€1659), with the highest costs incurred for hip (€15,833) and vertebral (€10,593) fractures. CONCLUSION: This study highlights a significant treatment gap in Spanish women aged ≥ 50 with a first FF or newly diagnosed PMO. Costs are particularly high for those with a first FF, especially for hip or vertebral fractures. Improving treatment adherence could reduce fracture risk, healthcare costs, and resource utilisation.