Objective: Adherence to tyrosine kinase inhibitor treatment is a significant factor in the achievement of a good clinical response in chronic myeloid leukemia (CML). The aim of this retrospective study is to investigate 1- and 2-year medication adherence to imatinib treatment, linking adherence rates with the clinical outcome, in accordance with European LeukemiaNet Recommendations for the management of CML. We have tried to find a cutoff value for adherence in order to achieve a good clinical outcome. Methods: The method used to calculate medication adherence was the ratio between the received and the prescribed daily dose. Results: We observed the levels of mean adherence for each of the following response groups (in years 1 and 2, respectively): complete response (0.96, 0.95), MR4.5 (1.00, -), MR4 (0.93, 0.91), major molecular responses (0.96, 0.97), warning (0.91, 0.89) and failure (0.79, 0.84). Conclusion: Results show that the higher the adherence, the lower the level of BCR-ABL1. Furthermore, using cutoffs ≥0.9, outcomes were significantly improved compared to those with cutoffs <0.90. This value of adherence is in line with previous publications.