Cytogenetic analysis performed at diagnosis is considered to be the most valuable prognostic factor in acute non-lymphocytic leukemia (ANLL), a very heterogeneous disease. Little data exist in Iran regarding the cytogenetic characteristics of ANLL . Therefore, cytogenetic investigations were performed for 58 patients with various subtypes of ANLL with unstimulated short term culture and high resolution cell synchronization techniques. Among the 58 evaluated patients, 45 (77.5%) showed clonal karyotypic abnormalities and the percentages of the abnormal cells were recorded within the range of 30%-100%. Some 14 were classified as M1, 20 as M2, 19 as M3 , 3 as M4, 1 as M5 and 1 as M6. The most common chromosome rearrangements were t(15;17), t( 8;21) and t(9;22). Trisomy of chromosome 8 (+8) was the most frequent numerical alteration in 3 patients with M1, M2 and M6. The incidence of other chromosomal defects, including -10, DMCs , -19 , 5q- , dicentric(dic), chromatid breaks, and marker chromosomes was relatively high. Similarities and dissimilarities of our study with others may be due to the role of genetic sensitivities as well as uneven geographic distribution in the pathogenesis of ANLL. Further prospective studies are warranted to precisely elucidate ethnic differences in the pathogenesis of this disease in different populations.