Chronic myeloid leukemia (CML) arises from the fusion of the BCR and the ABL1 genes. The BCR gene (chromosome 22q11.2) and the ABL1 gene (chromosome 9q34) fuse together due to reciprocal chromosome translocation forming the Philadelphia chromosome (Ph). This fusion gene codes tyrosine kinase which accelerates the cell division and reduces DNA repair. Imatinib mesylate is a selective inhibitor of this tyrosine kinase. It is the first-line treatment for CML-patients. However, it became clear that Philadelphia-positive (Ph+) cells could evolve to elude inhibition due to point mutations within the BCR-ABL kinase domain. To date more than 40 mutations have been identified and their early detection is important for clinical treatment. With the development of the new tyrosine kinase inhibitors (TKIs), associated with these mutations, the resistance problem seems to diminish, as some of the new drugs are less prone to resistance. The aim of this review is to focus on the diff erent mutations leading to resistance.