A case of CLL with two different cellular populations is reported. A 50-year-old man was evaluated for persistent absolute lymphocytosis. A peripheral blood smear revealed numerous small lymphocytes (83% of white blood cells counted). Frequent Grumpecht shadows were present, too. On bone marrow aspirate smears lymphocytes comprised 85% of the total cells counted, and the bone marrow biopsy showed a mixed nodular-interstitial infiltration pattern. The immunophenotypic study showed two different leukemic populations. The first one (comprising 79% leukemic cells) was CD5+, CD19+, CD10-, CD20+, CD18-, CD22-, CD23+ +, lambda dim, and FMC7-. The second population (comprising 21% leukemic cells) was CD5+, CD19+, CD10-, CD20+, CD18+, CD22+, CD23+, lambda+ +, and FMC7+. Gene rearrangement studies detected the germline and one rearranged band in Jk blot with each restriction endonuclease. In the Jh blot the germline and two rearranged bands were detected with EcoRI and BamHI and three rearranged bands with HindIII. The JBI/JBII blot detected only the germline band. The detection of three rearranged bands was interpreted as evidence of the presence of at least two monoclonal populations of cells with the same light chain restriction.