Thus, we suspected that our case highly likely had SMZL and the possibility of mantle cell lymphoma was ruled out from negative CCND1 staining and that of hairy cell leukemia from cell morphology and barely detectable CD25; however, we missed a chance by applying FISH procedures in the process of diagnosis to differentiate SMZL from other leukemia/lymphomas. This evidence concerns the gene CCND1 and hairy cell leukemia.