It is a phase 4 study, not randomised and multicentric. Within 2 months after the diagnosis, the patients daily receive imatinib by oral way during at least 1 year (260mg/m² once a day), i.e. until the cytogenetic analysis.

Beyond 1 year of treatment, if a haematological relapse or a loss of the cytogenetic response is observed, the nature of the treatment suggested to the patient is left with the appreciation of the investigator.

Later on, discontinuation of imatinib is discussed if a molecular remission (negative RT-PCR) is obtained and maintained for at least 2 years.

Inclusion Criteria:

• Old < 18 years, male or female.
• Chronic myeloid leukaemia confirmed on the cytogenetic level by the presence of the translocation t(9; 22) (q34; q11) or by the presence of transcript BCR-ABL in the event of absence of description of the translocation t(9; 22) (q34; q11).
• Chronic phase of a chronic myeloid leukaemia
• Absence of extra-medullary disease (except for a hepatomegaly and/or of a splenomegaly).
• Absence of any former treatment of chronic myeloid leukaemia except for hydroxyurea.
• Stop of hydroxyurea at least week before the beginning of the imatinib mesylate.
• Diagnosis of chronic myeloid leukaemia in chronic phase recent (less than 2 months).
• Score of Lansky ≥ 60.
• Effective contraception among patients in age to procreate.
• Written voluntary informed consent of the two parents or the legal guardian.

Exclusion Criteria:

• Patients with grade 3 / 4 cardiac disease.
• Pathology cardiac, pulmonary, hepatic, renal or neurological of grade > 2 (WHO).
• Participation in a clinical trial in the 28 days preceding the beginning by the treatment.
• Impossible Follow-up during at least 2 years, patient not compliant.
• Expectant mother or nursing.