The human CD8 molecule is usually expressed on T lymphocytes or natural killer cells but not on normal B cells. Over a course of 5 years, we followed a case of B-CLL which aberrantly expressed the CD8 molecule. During this period, the clinical and hematological conditions of the patient were stable. This B-CLL presented a typical immunophenotype (HLA DR+, CD19+, CD5+, CD23+) with monotypic expression of surface immunoglobulin light chain kappa. We confirmed the CD8 expression on these leukemia cells by using double labelling and different antibodies directed against this antigen. We measured the quantitative expression of the CD8 molecule. The number of CD8 molecules per cell was clearly lower on these malignant B cells than on normal T lymphocytes. In order to evaluate the prognostic significance of this CD8 expression, we quantitated in parallel other markers such as CD5, CD23, CD22, CD11c. During 5 years, this aberrant CD8 expression persisted and was associated with an increase of the CD23 and a decrease of CD22 levels, known to correlate with a good prognosis in agreement with the karyotype analysis. Altogether our results led us to conclude that the aberrant CD8 expression in this case of B-CLL may correlate with a non-aggressive form of lymphoproliferative disorder.