We report an unusual case of hairy cell leukemia variant with IgA and IgG-lambda biclonal gammopathy exhibiting light chain and a surface immunoglobulin class different from that of the paraproteins. In addition, we documented by gene rearrangement study that the hairy cell leukemia variant clone appears independent from the paraprotein-producing cells. The kappa light chain was expressed on the surface of hairy cell leukemia variant cells. Southern blot analysis revealed rearrangement of the kappa-light-chain gene and germline configuration of lambda-light-chain gene. We observed significant clinical improvement and reduction in the leukemic infiltrate in the patient after treatment with 2-chlorodeoxyadenosine (2-CdA). The intensity of the rearranged kappa-light-chain gene band decreased with therapy and increased at relapse without significant change of the paraproteins. Previously reported cases of hairy cell leukemia variant with paraproteins are reviewed, and our patient's contribution to the understanding of this association is stressed.