Relevance: Chronic myelogenous leukemia (CML) patients represent the heterogeneous group. Several studies in recent years were aimed to personalize treatment based on individual patients characteristics. Aim of study: The aim of our study was to assess prognostic value of individual BCR-ABL decline rate in the first three months of CML therapy to predict optimal response. Patients and methods: Fifty-four patients with chronic phase CML were included in the study. Forty-one patients started treatment with Imatinîb 400 mg/day, 12 patients started with Nilotinib 600 mg/day and 1 patient started with Dasatinib 100 mg/day. BCR-ABL level was determined by International Scale at the moment of diagnosis and after 3,6 and 12 months with ITK therapy. The ratio of BCR-ABL levels at 3 months to baseline for each patient, frequency of the achievement of the early molecular response at 3 months (10% by IS) and MMR at 12 months were assessed; in addition, we calculated ratio of BCR-ABL levels at 3 months to BCR-ABL levels at 1 month. Twenty-six out of 34 patients (76.5%) with ratio of BCR-ABL levels at 3 months to baseline below than 0,1 achieved MMR at 12 months, while only 9 out of 20 patients (45%) with ratio more than 0,1 had optimal response (p = 0.02). Ratio of BCR-ABL levels at 3 months to BCR-ABL levels at 1 month showed much better results with the same (0.1) cut-off value - 5 out of 6 patients (83.3%) with ratio BCR-ABL levels at 3 months to BCR-ABL levels at 1 month below than 0.1, while only the 1 patient (16.7%) with ratio more than 0.1 achieved optimal response (p = 0.04), respectively. Application of early molecular response at 3 months (10% by IS) yielded worse discrimination results: 33 of 46 (71.7%) patients with BCR-ABL level ≤ 10% at 3 months, whereas 2 of 8 (25%) patients with BCR-ABL > 10% had MMR at 1 year (p = 0.02), respectively. Furthermore, application of our ratio cut-off value in patients with early molecular response (BCR-ABL level ≤ 10% at 3 months) allowed us to reveal additional 5 high-risk patients who have not reached MMR after 1 year of therapy. Conclusion: Our study showed that individual BCR-ABL level decline rate estimated in the first three months of CML therapy from the baseline to the level measured at 3 months might be useful as an optimal predictor of outcome for CML patients (MMR after 1 year of treatment).