Hairy cell leukemia (HCL) patients could have an excellent prognosis with adequate treatment. Treatments are not generally curative but are extremely effective in inducing long-lasting clinical remissions. An observational retrospective study was conducted on a single-center registry of 144 patients with a median follow-up of 11.5 years, focusing on long-lasting continuous first complete remissions (CR) wondering if patients can be cured only with front-line approach. CR for more than 5 years after first-line therapy were found in 22.2 \% cases. The median duration of response was 9.8 years, while for relapsed patients, the first response had a median duration of 2.4 years. Three different subsets of long-lasting first CR were identified: 15 patients are between 5 and 10 years with a median duration of CR of 6.5 years; 7 patients are between 10 and 15 years with a median duration of CR of 12.3 years; and 10 patients present a follow-up superior to 15 years with a median duration of CR of 20.0 years. There is a need for continuous study in this field to better define the optimal therapeutic regimen and, in particular, the biological issues since at least 20-25 \% of HCL patients can be cured with only one treatment.