Hairy cell leukemia (HCL) is a rare hematologic malignancy with high response rates and long progression-free survival (PFS) after treatment with purine nucleoside analogs (PNAs; Pentostatin/Cladribine). However, treatment is not curative, and subsequent treatment at relapse is often required. Rechallenge with a purine analog is commonly implemented despite limited data regarding the efficacy of this approach. We retrospectively analyzed 61 consecutive patients with HCL diagnosed between 1995 and 2013 at Cleveland Clinic. Median follow-up was 72 months (3-193). Cladribine as first-line therapy was administered to 59 patients (97%). Overall response rate (ORR) was 97%, with 78% of patients achieving complete remission (CR). PFS after response was significantly improved for patients who achieved CR compared with those with a partial remission (PR) (5-year PFS 71% vs. 39%, respectively [P = .004]). Of the 19 patients who relapsed, 12 received PNAs as second-line treatment with an ORR (83%) comparable to what these patients had with first-line treatment (ORR 92%). Overall survival of all 61 patients was excellent and superior to that of age-, sex-, and race-matched controls from the general population, possibly due to selection bias. In an analysis of a larger cohort of unselected patients in the Surveillance, Epidemiology, and End Results (SEER) database, we found that mortality rates for patients with HCL were similar to those of the general population approximately 5 years after diagnosis. These data confirm the excellent prognosis for patients with HCL after first- and second-line PNA therapy.