INTRODUCTION: Multiple myeloma (MM) is a malignancy of plasma cells; most MM patients will eventually relapse or become refractory to treatment. Treating MM patients remains a challenge since patients eventually progress through several lines of therapy (LOTs), requiring the use of multiple MM drug classes. We examined healthcare resource utilization (HCRU) and the costs incurred by MM patients following triple class exposure (TCE; defined as exposure to a proteosome inhibitor, an immunomodulatory agent, and an anti-CD-38 antibody). METHODS: Adult MM patients were selected from the MarketScan® commercial and Medicare supplemental databases (January 2009-February 2021). From this cohort, patients who had TCE and ≥ 1 subsequent LOT that occurred after January 1, 2017 were included in the study population. The initiation date for the first post-TCE LOT was defined as the index date. All-cause and MM-related HCRU and the associated costs were examined post-index date. RESULTS: A total of 85 MM patients with TCE who initiated ≥ 1 subsequent LOT post-TCE and had ≥ 1 year of follow-up post-index date were included in the study population; mean age on index date was 58.8 years, and 60.0% were male. The time from first-observed MM diagnosis until index date averaged 47.5 months. During an average follow-up of 20.9 months post-index date, 64.7% of patients (N = 55) initiated a second LOT and 35.2% (N = 30) received at least 3 LOTs. During follow-up, mean total all-cause healthcare cost per patient was $722,992 (equivalent to $34,578 per patient per month [PPPM]). Approximately 90.7% ($655,524 per patient) of the total all-cause healthcare costs were MM related, 66.0% of which were MM drug/infusion costs. CONCLUSION: In this real-world US study, MM patients with TCE incurred high healthcare costs, with the majority being MM related and primarily attributed to MM drug and infusion costs.