Balanced translocations and chromosomal rearrangements are rare events involved in acute lymphoblastic leukemogenesis, yet little is known about the actual gene anomalies responsible for it. These rearrangements are reflected by the expression of certain surface markers such as KOR-SA3544 for t(9,22) and NG.2 for 11q23 rearrangements and may indicate a poor prognosis. Our purpose was to investigate whether these immunophenotypical and cytogenetical markers also correlate with cytogenetical molecular abnormalities. Bone marrow aspirate and peripheral blood samples were available for imunophenotyping and standard cytogenetic analysis. Initially we have investigated by imunophenotyping 28 patients with acute lymphoblastic leukemia, admitted in the Department of Hematology during the last year. Out of 28 cases, 15 were diagnosed as B-lineage ALL. Of those 15 patients, 7 had pro-B acute lymphoblastic leukemia immunophenotype: CD19+CD10+CD34+. Reactivity with KOR-SA3544 was found in 8 patients with proB-ALL. A particular subset of 3 patients with proB-ALL associated simultaneously KOR-SA3544 and NG.2 detected following flow-cytometric, and t(9,22) after standard cytogenetic analyses. In particular, one of them had a complex karyotype, coexpression of myeloid markers (CD33) and a history of breast cancer. One case had a inv (16). Our results suggest that the coexpression of KOR-SA35443 and NG2 in result of karyotype abnormal changes may predict a poor prognosis. The detected molecular cytogenetic aberrations are not typical for ALL; they indicate genomic instability, which most probably contributed to the observed poor outcome.