B-cell acute lymphoblastic leukemia (B-ALL) accounts for 20-30% of acute leukemias in adults. Combined application of data from immunophenotyping, karyotyping and molecular analyses allows a better understanding of this heterogeneous disease. We studied 30 adult patients with newly diagnosed B-ALL by conventional cytogenetics, fluorescent in situ hybridization (FISH) and immunophenotyping analyses. We report statistically significant prevalence of structural aberrations (43%) over numerical changes (17%) (p=0.02). The most frequent structural changes were t(9;22)(q34;q11)/bcr-abl-17%, t(8q24)/C-MYC-10%, t(11q23)/MLL-6%, del 4p-6%, del12p-3%, and t(1;19)-3%. Complex karyotype was found in 17% and normal karyotype in 30%. The most frequent immunophenotype was of common B-ALL (43%), and cytogenetic and/or molecular abnormalities were found in 78% of them. We distinguished a relatively high incidence (17%) of mature B-ALL and 60% of them were associated with t(8;14)/C-MYC. We established association of cytogenetic aberrations with immunophenotype only in mature B-ALL. The other immunophenotypes are characterized by genetic heterogeneity and the presence of cytogenetic abnormalities unusual for adult B-ALL - trisomy 8 and t(1;19)(q23;p13).