Background:Chronic myeloid leukaemia (CML) is a clonal disease of a hematopoietic stem cell. The incidence of this disease is about 15% of leukemias and may be present at any age. The presence of the Philadelphia (Ph) chromosome confirms the diagnosis of CML. The expression of the Patched homolog 1 gene (PTCH1) has been proposed as a prognostic marker of imatinib response in chronic phase chronic myeloid leukaemia (CP-CML) patients. Aim: This study aimed to measure the level of PTCH1 protein in newly diagnosed CP-CML and to find correlation between its level in those patients and response to first line of treatment, imatinib and other prognostic factors. Patients and Methods: Our study enrolled 50 patients of newly diagnosed CP-CML. We have measured the level of PTCH1 protein initially once the patient diagnosed and after 6 months of treatment with imatinib by ELISA test. Results: There was highly significant difference between initial PTCH1 level and its level after 6 months of imatinib treatment (P=0.000). The level of PTCH 1 was correlated significantly with the molecular response both at the beginning of treatment with imatinib and six months later. (P=0.002), (p=0.001) respectively. Conclusion: To the best of our knowledge that we are the first to report on PTCH1 protein as a new diagnostic and prognostic marker in CP-CML patients.