The purpose of this study was to investigate the factors related to drop-outs from study participation, comparing intervention and comparison groups. Methods: The study was a descriptive study using the pretest data of an intervention study. Patients diagnosed with COPD (N=254) were included in the study. Characteristics and levels of depression, self-efficacy, and health related quality of life were compared between participant and drop-out groups using descriptive statistics, x2-test, and t-test. Results: For drop-outs in the intervention group, patients with high BODE (body-mass, airflow obstruction, functional dyspnea, and exercise capacity) Index, low body mass index, high perceived dyspnea, and poor health related quality of life in the activity domain tended to drop-out from the studies. Drop-outs from the control group were older patients and patients with shorter distance for 6 minutes of walking. Conclusion: The results of this study show that patients with poorer functional levels, especially in physical functioning, are more likely to drop-out from studies. These results indicate that, considering the poorer quality of life in patients with worse health conditions, there is a need for special attention and innovative strategies to assure patients with severe physical conditions are able to complete the interventions.