Aims and Objectives:This study aimed to investigate the effects of socioeconomic-, patient-, treatment-, condition-and health system-related factors on medication adherence in patients with chronic obstructive pulmonary disease (COPD).Background: Medication adherence is essential for the management of chronic diseases. The World Health Organization created a Multidimensional Adherence Model (MAM) and showed that medication adherence is affected by a combination of numerous factors.Design: A descriptive correlational study was conducted.Methods: A total of 114 patients with COPD were included. Data were collected on five dimensions based on the MAM framework. Medication adherence, self-efficacy and symptoms were evaluated using the Adherence to Refills and Medications Scale-7 (ARMS-7), COPD Self-Efficacy Scale (CSES) and COPD Assessment Test (CAT), respectively. The data were analysed using descriptive statistics, correlational statistics and structural equation modelling. The STROBE checklist was used. Results:The ARMS-7 scores were associated with the body mass index of patients (F = 4.245, p = .017), smoke pack-years (r = .277, p = .004) and the CSES total score (β = -0.249, p = .002) in patient-related factors. The ARMS-7 score was not associated with socio-economic and health system-related factors. The ARMS-7 score showed a significant correlation between COPD diagnosis duration (r = −.276, p = .003) and the total number of drugs (r = −.215, p = .022) in treatment-related factors. The ARMS-7 scores were associated with the number of comorbid illnesses of patients with COPD in condition-related factors (F = 3.533, p = .033). Conclusion:This study showed that medication adherence in COPD was mostly affected by patient-, treatment-and condition-related factors.Relevance to clinical practice: Healthcare professionals should establish training and counselling programs to increase the medication adherence level of patients, particularly for patients who are newly diagnosed, require multiple drugs and have comorbid diseases or low self-efficacy.