Hairy cell leukemia (HCL) is a rare type of indolent B-cell leukemia, characterized by symptoms of fatigue and weakness, or-ganomegaly, pancytopenia, and recurrent opportunistic infections. Classic HCL should be considered a distinct clinical entity separate from HCLvariant (HCLv), which is associated with a more aggressive disease course and may not respond to standard HCL therapies. Somatic hypermutation in the IGHV gene is present in most patients with HCL. The BRAF V600E mutation has been reported in most patients with classic HCL but not in those with other B-cell leukemias or lymphomas. Therefore, it is necessary to distinguish HCLv from classic HCL. This manuscript discusses the recommendations outlined in the NCCN Guidelines for the diagnosis and management of classic HCL.