Imatinib is widely recognized as the standard of care in the first-line treatment of chronic myeloid leukemia (CML); however, resistance can limit its long-term benefits. Early identification of the loss of response to imatinib is therefore important for the optimal management of patients with this type of leukemia. Cytogenetic and molecular responses during the first 12 months of treatment have been shown to predict future responses (complete cytogenetic response and major molecular response) and reduce disease progression. The degree of early reduction in BCR-ABL levels after commencing imatinib therapy is a good indicator of subsequent response. Monitoring for kinase domain mutations should also be considered in patients with suboptimal response or in those who demonstrate resistance. Modification of the treatment strategy is required if there is a loss of response. Dasatinib and nilotinib are the most extensively studied second-generation BCR-ABL tyrosine kinase inhibitors, and are currently approved for treating patients following imatinib failure.