Background: Acute lymphoblastic leukemia (ALL) is the sixth most common malignancy in Iran. Cytogenetic analysis of leukemic blasts plays an important role in classification and prognosis in ALL patients. The purpose of this study was to define the frequency of chromosomal abnormalities of ALL patients in adults and children in Fars province, Iran.Methods: In this cross-sectional study, we evaluated karyotype results of bone marrow specimens in 168 Iranian patients with ALL (154 B-ALL and 14 T-ALL) in Fars Province using the conventional cytogenetic G-banding method.Results: The frequency of cytogenetic abnormalities, including numerical and/or structural changes, was 61.7% and 53.8% in the B-ALL and T-ALL patients, respectively. Hyperdiploidy was the most common (32%) cytogenetic abnormality. Among structural abnormalities, the most common was t(9;22) in 11% of the patients. The children showed a higher incidence of hyperdiploidy and lower incidence of t(9;22) than adults (P<0.05). We found a lower incidence of recurrent abnormalities such as 11q23, t(1;19), and t(12;21) than those reported in previous studies.Conclusion: Normal karyotype was more frequent in our study. The frequencies of some cytogenetic abnormalities such as hyperdiploidy and t(9;22) in our study were comparable to those reported in the literature. The results of this study in Fars Province can be used as baseline information for treatment decision and research purposes in ALL patients. We recommend the use of advanced molecular techniques in the future to better elucidate cryptic cytogenetic abnormalities.