Objective: To determine the role of immunophenotyping in chronic lymphocytic leukemia 
(CLL) patients at South Egypt Cancer Institute (SECI). Methodology: This study was carried 
out in Department of Clinical pathology, South Egypt Cancer Institute, from December 2017 
to July 2019. We used SECI Flowcytometry lab 4 color for diagnosis. Results: 37 patients 
were included in our study with CLL and 30 apparently healthy control group. For the both 
groups we performed: CBC, BM aspiration, BM biopsy and immunophenotyping. The mean 
age in CLL group was (55.92± 9.02) years. while the mean age in control group was (38.37 ± 
14.08) years . Conclusion: Immunophenotyping has a great role in CLL diagnosis.