Nonadherence is common in patients with chronic myeloid leukemia (CML) and leads to treatment failure and poor outcomes. Side effects due to treatment are also common in patients with CML. However, no study has investigated the link between side effects and medication adherence for patients with CML in Taiwan. Therefore, the aim of our study was to explore the influence of side effects on medication adherence in Taiwanese patients with CML.CML in chronic-phase patients treated with breakpoint cluster region-Abelson murine leukemia viral oncogene homolog 1 tyrosine kinase inhibitors were recruited. We designed a questionnaire to collect baseline patient information, medication adherence (measured using the 8-item Morisky Medication Adherence Scale), and side effects. Clinical outcomes were assessed by the 3-month early molecular response rate and the 12-month major molecular response rate. Statistical comparisons of different parameters between adherent and nonadherent groups were conducted.Fifty-eight patients were enrolled in this study, and 31% of them had poor adherence. The lack of information about treatment and medication was the major reason for poor medication adherence. Patients who were younger and unmarried were prone to poor adherence. The occurrence of side effects carried no statistically significant influence on adherence. Poor adherence resulted in a poor treatment response (lower 3-month early molecular response rate and lower 12-month major molecular response rate).Poor adherence is common in Taiwanese patients with CML. The main reason for a decrease in the adherence rate is the lack of comprehensive information about treatment and medication, particularly in young and single population. The next urgent step is to educate patients about their treatment and management of side effects to improve adherence and treatment outcome for patients with CML in Taiwan.