Purpose The aim of this study was to verify whether the distribution of a treatment diary by a pharmacist could influence the adherence to oral treatment with imatinib, nilotinib, and dasatinib in patients with chronic myeloid leukaemia. Methods The level of adherence was calculated using the received daily dose/prescribed daily dose ratio and compared between patients who used a diary and those who did not. Results Forty-four (35.8%) of 123 patients with chronic myeloid leukaemia completed the diary: 20 (45.4%) receiving imatinib, 17 (38.6%) receiving nilotinib, and seven (15.9%) receiving dasatinib. Treatment adherence with the diary calculated using received daily dose/prescribed daily dose method was 93.6% (imatinib 94.9%, nilotinib 91.1%, and dasatinib 95.8%). Adherence during the period without a diary was 86.5% (84.9, 87.4, and 90%). Adherence was significantly greater with than without a diary (p < 0.0001). Conclusions The findings of this study that, in the case of chronic diseases, direct pharmacist-patient contact is important in order to maintain high levels of adherence, and a treatment diary is a valid means of doing this. According to these data, it is necessary to support similar patient-oriented programmes in order to ensure high levels of adherence and optimize drug management.