The aim of this study was to evaluate the heterogeneity of immunophenotype features in acute leukemia patients and to detect the presence of leukemia-associated immunophenotypes. We prospectively investigated the phenotype of blast cells from 44 adult acute leukemia patients using a large panel of monoclonal antibodies by multiparametric flow cytometry. Thirty-three patients were classified as AML according to the FAB classification. Eleven patients were diagnosed as ALL (10 cases B-ALL, 1 case T-ALL) according to both FAB and immunnophenotyping. We found leukemia-associated phenotypes in 28 of 33 AML patients (84.8%) and in 8 of 11 ALL patients (72.7%). In 61.1% of patients more than one aberrant phenotype was observed. Linear infidelity was the most frequent aberrancy in both AML (64.3%) and ALL (37.5%) subgroups. The present study shows that MFC is a helpful method for sufficient identification of leukemic cells and for determination of blast cells immunophenotype heterogeneity. The double stain flow cytometry in our study revealed aberrant phenotypes in up to 81.8% patients.