Abstract Background and Purpose Imatinib therapy shows excellent efficacy for chronic myeloid leukemia (CML) patients. The five-year overall survival of chronic-phase CML patients treated with imatinib can be expected to reach over 90%. Now, the goal of therapy has become the achievement of therapy-free remission (TFR) for most patients. However, predictive markers for achieving deep molecular response (MR) or TFR are yet to be elucidated. The recently published European LeukemiaNet recommendations 2013, which are mostly based on Caucasian studies, show the importance of an early response at 3 months or 12 months after starting imatinib treatment to assess optimal response. Using the registry of our study group, we assessed whether early cytogenetic or molecular responses at 3 months and 12 months after starting imatinib are associated with the achievement of deep MR or long-term outcome in Japanese CML patients. Patients and Method We reviewed 135 CML patients in the registry of our study group. Imatinib was started between December 2001 and June 2008. We retrospectively analyzed 92 CML patients (35 patients with prior therapy before imatinib) who could be assessed for partial cytogenetic response (PCyR: Ph<35% or bcr/abl transcript <10%) at 3 months after starting imatinib treatment, and 81 patients (25 patients with prior therapy before imatinib) who could be assessed for major molecular response (MMR: bcr/abl transcript <10% or 300 copies/μg) at 12 months in our multicenter observation study group. The clinical data was reviewed in August 2010. We excluded patients who had been switched from imatinib to a second tyrosine kinase inhibitor (TKI) before August 2010. We compared overall survival and the cumulative achievement of deep MR (negative bcr/abl transcript by PCR or the TMA-HPA method) between patients with and without PCyR at 3 months, also between patients with and without MMR at 12 months. The probability of overall survival and the cumulative incidence of deep MR were calculated by the Kaplan-Meier method and compared by the log-rank statistic. Results Seventy-six out of 92 patients (82.6%) achieved PCyR at 3 months. Forty out of 81 patients (49.3%) achieved MMR at 12 months. The patients with PCyR at 3 months showed significantly better overall survival (p=0.004) and higher cumulative achievement of deep MR (p=0.009) than the patients without PCyR. Overall survival between the patients with and without MMR at 12 months did not show a significant difference (p=0.06). However, the patients with MMR at 12 months showed significantly higher cumulative achievement of deep MR (p<0.001) than the patients without MMR. Conclusion Early cytogenetic and molecular responses at 3 months and 12 months after starting imatinib are also predictive factors for good prognosis and the achievement of deep MR in a registry of Japanese patients. Our data confirm the criteria of optimal response in European LeukemiaNet recommendations 2013 was appropriated for Japanese CML patients in practical setting. Disclosures: No relevant conflicts of interest to declare.