Genetic changes associated with Acute Lymphoblastic Leukaemia (ALL) provide diagnostic and prognostic information with a direct impact on patient management. We report the cytogenetic analysis of 298 Tunisian patients with ALL, including 183 children and 115 adults. Chromosome abnormalities have been detected in 68.2% of our patients associating clonal numerical and/or structural rearrangements. Some chromosomal abnormalities especially hyperdiploidy, 19p13 abnormalities, 8q24 translocations, 12p, 6q deletions and TCR rearrangements occur at a lower incidence compared to that reported in other populations. ALL cases (5.7%) had miscellaneous clonal abnormalities. We also found in our Tunisian series a higher incidence for T-lineage ALL more than usually described. Among structural chromosomal abnormalities, t(9;22)(q34;q11) resulting in the BCR/ABL fusion and the t(12;21)(p13;q22) resulting in the TEL/AML1 fusion were studied by FISH providing additional diagnostic and prognostic information. We conclude that although the incidence of our cytogenetic results are slightly different, their clinical significance is similar to that described in the literature.