Acute myeloid leukemia (AML) is a clonal disorder caused by malignant transformation of hematopoietic stem cells in bone marrow. Untreated illness causes death due to abnormal hematopoesis and overproduction of undifferentiated cells (blasts). Mutations causing AML mainly occur in genes coding for signaling pathway proteins, transcription factors and epigenetic regulators with varying clinical outcome depending on types of acquired chromosomal abnormalities. Locus 11q23 codes for MLL (mixed lineage leukemia) gene, ortholog of trithorax protein in fruitfly (Drosophila melanogaster), which is a transcription factor and regulator of HOX genes. So far it has been found that MLL gene is involved in 85 different translocations and that it forms 66 fusions with various partner genes. Changes of 11q23/MLL locus have been associated with very poor clinical outcome. The goal was to detect and describe specific changes of MLL gene in AML positive patients using interphase FISH method as well as classical cytogenetic analysis. Results showed that different changes of MLL locus can be detected using one locus specific probe (Vysis). I-FISH method proved to be indispensable in diagnosis of MLL gene changes that could not be detected using classical cytogenetic analysis. Translocations were found to be the most common chromosomal alterations associated with MLL locus. It was also found that MLL rearrangement has the highest incidence in AML-M5b subtype based on FAB classification of AML.