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.