This study on patient's compliance in clinical workaday life aims to assess and to improve CML treatment in Germany by means of adherence supporting measures and to increase adherence awareness by physicians and patients.

Inclusion Criteria:

• Adult (> 18 years) CML patients in the chronic phase
• Medical history of cytogenetically confirmed CML-CP by the presence of the Philadelphia chromosome on bone marrow aspirates (a minimum of 20metaphases is required; FISH cannot be used); Philadelphia chromosome negative but BCR- ABL-positive CML patients can be included
• ECOG performance status of < 2
• Imatinib treatment for at least 1 year and showing CCyR or MMR
• Prior treatment with chemotherapeutics such as hydroxyurea or interferon- alpha is allowed
• Prior periods of accelerated phases are allowed
• Negative pregnancy test for female patients of childbearing potential within 7 days before initiation of study drug
• Ability to understand and willingness to sign a written informed consent document prior to any study related screening procedures
• Written informed consent, including the consent to be called for interviews by the external, neutral institution.

Exclusion Criteria:

• Patients with prior blast crisis or stem cell transplantation
• Patients with severe medical condition(s) that in the discretion of the investigator prohibits participation in the study (e.g., clinically significant heart diseases, uncontrolled diabetes, active or uncontrolled infection, impaired gastrointestinal function/diseases)
• Treatment with drugs or substances, especially those known to modify the cytochrome P450 activity, should be either discontinued or exchanged by different medication (see link for complete list of these medications: http://medicine.iupui.edu/flockhart/table.htm.)
• Pregnant or breastfeeding women
• Male or female of childbearing potential unwilling to use contraceptive precautions throughout the trial