Background: Purine nucleoside analogs (PNAs) are highly effective for first-line treatment of hairy cell leukemia (HCL). In clinical trials of single PNAs, several adverse events (AEs) were reported; however, little is known regarding the costs and healthcare resource utilization (HRU) resulting from AEs in HCL patients (pts) treated with PNAs in non-clinical trial settings. Objective: Determine the costs and HRU of high incident and clinically important AEs associated with PNA therapy in HCL pts in the Truven MarketScan database. Methods: Adults (aged ≥18 years) with ≥2 HCL diagnosis codes ≥30 days apart during January 1, 2006–December 31, 2015 were included. Pts had ≥1 prescription claim for a PNA (cladribine or pentostatin ± rituximab) after HCL diagnosis date. First PNA claim date was defined as the index date. Pts had continuous health plan enrollment for ≥6 months at baseline and ≥12-months follow-up with no PNA in the baseline period. Pts were placed into cohorts based on the occurrence of myelosuppression (MSPN) and opportunistic infections (OI) as these were highest incident and clinically important AEs observed. Generalized linear models were used to compare outcomes during the 12-month follow-up. Results: Of the 219 pts with no history of MSPN, 101 developed MSPN (incidence [I]: 461 per 1000 pt-years) and of 619 pts with no history of OI, 26 developed OI (I: 42 per 1000 pt-years). Demographics were similar between pts with and without MSPN and OI. Pts who developed OI or MSPN had significantly higher inpatient admissions and costs (Table 1). Conclusions: PNA-treated HCL pts who developed MSPN or OI incurred higher HRU than those who did not develop either condition. This indicates the need for new therapeutic strategies to reduce HCL-treatment-associated toxicities.