CCND1-IGH@ translocation is considered pathognomonic of mantle cell lymphoma (MCL), as this distinct chromosomal abnormality has not been reported in any other subtypes of mature B-cell lymphoma. Despite this unifying cytogenetic feature, MCL encompasses 2 distinct groups: the usual MCLs with an overall survival of 3 to 5 years and the so-called "indolent non-nodal mantle cell lymphomas (INNMCLs)." The latter group of MCLs has quite distinctive clinical features, including frequent neoplastic lymphocytosis, absent peripheral lymphadenopathy, and indolent clinical courses. The clinical, biological, and molecular characteristics of INNMCL are still not well understood. Herein, we report a patient with clinical and cytogenetic features of INNMCL with overlapping morphologic and immunophenotypic features resembling hairy cell leukemia (HCL). After failing the chemotherapeutic regimen for MCL, he received a HCL-directed therapy and achieved durable response. This case suggests that CCND1-IGH@ may rarely occur in other mature B-cell neoplasms such as HCL. Further clinicopathologic studies of the so-called "INNMCL" are warranted.