In this study our purpose was to define chromosomal aberrations and CD38 expression in male siblings 69 and 66-years-old with B-cell chronic lymphocytic leukemia (B-CLL). Cells from peripheral blood were analysed by comparative genomic hybridization (CGH) and fluorescence in situ hybridization (FISH). The alteration detectable by CGH was the over-representation of the Y chromosome in both samples. Interphase FISH were performed using locus (13q14 and 17p53) and centromere (chromosome 12, 17 and Y) specific DNA probes. One brother (patient 1, 69 years of age) showed deletion of the 13q14 region, this alteration was associated with low CD38 expression, both predicting a favourable prognosis. However, the younger patient's (patient 2, 66 years of age) cells expressed CD38 in high percent, which is considered as an indicator of poor prognosis, and deletion of the 13q14 was not seen. Other, relatively frequent chromosomal alterations including trisomy 12 and deletion of 17p53 were not present in any of the samples. The cytogenetic findings and the CD38 expression are in concordance with the clinico-pathological data of the siblings. Thus, we found the variability of these parameters described in B-CLL even in the familial form of the disease.