This study was conducted on 41 Egyptian children aged between 5 months and 12 years with newly diagnosed ALL, during a period of 15 months. By immunophenotyping, 15 cases were early pre-B ALL (36.6%), 11 cases pre-B ALL (26.8%), one case B-cell ALL (2.4%), and 14 cases T-cell ALL (34.2%). The frequency of the T-cell ALL was significantly higher than western countries, but similar frequencies were reported in Israel, South Italy, Greece, and Bulgaria (Left table ), supporting the hypothesis that geographical factors could be implicated in the pathogenesis. In this study, cytogenetic abnormalities were seen in 22 cases (53.6%). Hyperdiploidy was evident in 10 cases (24.4%) while hypodiploidy in 5 cases (12.2%). The most common structural chromosomal abnormalities were: t(l ;19) in 2 cases (4.9%), t(4;l 1) in 2 cases (4.9%), t(9;22) in one case (2.4%), t(8;14) in one case (2.4%), and t( 11 ; 14) in one case (2.4%). The frequency of all these cytogenetic abnormalities agree with the published data except for the slightly higher frequency of t(4;l 1), but this difference might be due to the small number of patients included in the present study. By RTPCR, 6 cases (14.6%) were TEL-AML1 positive. All were between the age of 2 and 6 years and with a TLC that ranged between 7.1 and 78.8 x Vf/nL. Two of them were early pre-B and the remaining four were pre-B ALL, all were CD10 positive and with a normal karyotype. There is a wide discrepancy in the frequency of TEL-AML1 in childhood ALL allover the world. The frequency in the present study is comparable to the western countries among the B-lineage group (22.2%) (Right table), but is much lower among the whole group of pédiatrie ALL patients (14.6%), possibly due to the higher frequency of T-cell ALL. At the present time the same group of children are being followed up for relapse. Country T cell ALL Country TEL-AML1 Egypt 34.2% Egypt 22.2% Israel 30% USA 26-32% South Italy 28.1% France 23% Greece 26% Germany / Italy 22-29% Bulgaria 28% Czech Republic 21% USA 13-15% China/Taiwan 19% United Kingdom 11% Japan 16-20%.