Cytogenetic analysis performed at diagnosis is considered to be the most valuable prognostic factor in acute nonlymphocyticleukemia (ANLL), a very heterogeneous disease. Little data exist in Iran regarding the cytogeneticcharacteristics of ANLL . Therefore, cytogenetic investigations were performed for 58 patients with various subtypesof ANLL with unstimulated short term culture and high resolution cell synchronization techniques. Among the 58evaluated patients, 45 (77.5%) showed clonal karyotypic abnormalities and the percentages of the abnormal cellswere recorded within the range of 30%-100%. Some 14 were classified as M1, 20 as M2, 19 as M3 , 3 as M4, 1 as M5and 1 as M6. The most common chromosome rearrangements were t(15;17), t( 8;21) and t(9;22). Trisomy ofchromosome 8 (+8) was the most frequent numerical alteration in 3 patients with M1, M2 and M6. The incidence ofother chromosomal defects, including -10, DMCs , -19 , 5q- , dicentric(dic), chromatid breaks, and markerchromosomes was relatively high. Similarities and dissimilarities of our study with others may be due to the role ofgenetic sensitivities as well as uneven geographic distribution in the pathogenesis of ANLL. Further prospectivestudies are warranted to precisely elucidate ethnic differences in the pathogenesis of this disease in differentpopulations.