Background: Hematopoietic cell transplantation (HCT) is a medically complicated, expensive and resource intensive medical technology. High health care costs are usually associated with high Out-of-Pocket (OOP) costs. In this population-based study, using deidentified administrative claims data from OptumLabs Data Warehouse, we describe total and patient level costs for one-year pre and post HCT and describe the characteristics of those with top 25% cost. Methods: Patients who had undergone an autologous or allogeneic HCT in 2015 to 2019 and had continuous health plan coverage for one year prior and post the index date-the date of the first claim for HCT, were included. We examined total costs, patient paid (OOP) and plan paid costs for one year before and after HCT. We also examined inpatient, outpatient, and pharmacy costs for the one year before and after the HCT. Logistic regression models examined factors including age, gender, race/ ethnicity, Charlson comorbidity index, geographic region and costs in the year prior to HCT (baseline costs) for their association with high total costs and high OOP costs (top 25%). Results: A total of 3,346 patients (2,344 commercial plan (CPE) and 1,002 under Medicare Advantage plan (MAPE) enrollees) were included in the study. Median one year post HCT costs for CPE was $ 612,517 (IQR 413,348- 960,456) and for MAPE was $ 521,000 (IQR 347,388-736,685). Median one year post HCT OOP costs were $ 5,407 (IQR 1,584 -10,000) in CPE and $7,199 (IQR 3,485 -16,396) in MAPE group. 625 subjects in the CPE and 253 subjects in MAPE group had overall costs in the top 25%. Median baseline costs were $482,107 vs. $846,943 in the low vs. high cost group in CPE and $278,656 vs. $343,633 in MAPE. There was a low correlation between OOP costs and overall costs (r = 0.17 for CPE and 0.15 for MAPE; p < 0.05). Younger age (OR for age 0.98; p < 0.001) and higher baseline costs (OR1.89; p < 0.001) predicted top 25% total costs post HCT in the CPE group. Not being African American (OR for African American 0.5; p = 0.02) and higher baseline costs (OR 1.07; p < 0.001) predicted top 25% total costs post HCT in MAPE group. Age (OR 0.97; p < 0.001), not being African American (OR 0.5; p = 0.001) and high baseline costs (OR 1.44; p < 0.001) also predicted higher OOP costs in the CPE group. The only factor that was associated with lower likelihood of OOP costs in top 25% in MAPE group was being Hispanic (OR 0.6; p = 0.004). Conclusions: HCT is an expensive treatment modality. High costs prior to HCT are associated with high post HCT costs both for patients on commercial and Medicare Advantage plan. The magnitude of correlation between patient level and total costs was low, likely due to differences in benefit plan. A careful assessment of benefits and costs of HCT is needed for providing high-value care and allow optimum allocation of the finite resources while minimizing patient level financial burden.