POEMS syndrome is a rare plasma cell disorder characterized by peripheral neuropathy, monoclonal gammopathy, and high levels of serum vascular endothelial growth factor, the pathogenesis of which remains unclear. A unique feature of this syndrome is that the proliferating monoclonal plasma cells are essentially lambda-restricted. Here we determined complete nucleotide sequences of monoclonal immunoglobulin lambda light chain (IGL) variable regions in 11 patients with POEMS syndrome. The V-region of the Ig lambda gene of all 11 patients was restricted to the V lambda 1 subfamily. Searching for homologies with IGL germlines revealed that 2 germlines, IGLV1-44*01 (9/11) and IGLV1-40*01 (2/10), were identified, with an average homology of 91.1%. The IGLJ3*02 gene was used in 11 of 11 re-arrangements with an average homology of 92.2%. These data suggest that the highly restricted use of IGL V lambda 1 germlines plays an important role in the pathogenesis of POEMS syndrome.