In the present study the karyotyping technique and the relatively new technique of fluorescence in situ hybridization (FISH) are employed to find the possible incidence of trisomy 12, Rb1 gene deletion and p53 gene deletion in 30 Egyptian CLL patients. Karyotyping revealed cytogenetic lesions in two cases (6.67%) while the FISH technique revealed cytogenetic lesions in 15 cases (50%). It is advisable to use the FISH technique as a routine investigation in chronic lymphocytic leukemia (CLL) cases.