BACKGROUND Chronic obstructive pulmonary disease (COPD) is one of the most important causes of morbidity and mortality worldwide. The complications of COPD are numerous, and cognitive impairment is one of the most common complications that relates to mortality and morbidity directly. The present study was conducted with the aim of evaluating the prevalence of cognitive impairment in patients with COPD in comparison to normal individuals. METHODS In this case-control study, 87 patients with COPD, whose diagnoses were confirmed by a pulmonologist based on the spirometry test findings, were included. The mini-mental state examination (MMSE) questionnaire was administered for assessing the cognitive impairment. Arterial oxygen saturation was measured. The MMSE questionnaires were administered to 60 healthy, age-and-sex-matched individuals without a history of myocardial infarction or cerebrovascular infarction, and their arterial oxygen saturations were measured. The data were analyzed using the SPSS (version 20) software. RESULTS In the case group, 42 patients (48.27%) had no cognitive impairment, 39 (44.82%) had mild, and 6 (6.89%) had moderate cognitive impairment. In the control group, 38 (63.33%) had no cognitive impairment, 20 (33.33%) mild and 2 (3.33 %) moderate cognitive impairment. There were significant relationships between the cognitive impairment and arterial oxygen saturation, severity of COPD, and higher age. The prevalence of cognitive impairment was 51.71% in the case group and 36.66% in the control group. CONCLUSIONS According the results of the present study, COPD increased the risk of cognitive impairment significantly and is related to the severity of COPD, arterial oxygen saturation, and higher age.