Airway obstruction is variable in asthma, while it is progressive and persistent in chronic bronchitis and emphysema. However, some of the patients presenting with symptoms of chronic airway diseases have clinical features of both asthma and COPD. The group with “Asthma–COPD Overlap Syndrome” (ACOS) phenotype was characterized by definitely irreversible airway obstruction accompanied by symptoms and signs of reversibility. In this study, we aimed to classify obstructive airway diseases by clinical, radiological, and pulmonary function tests. Patients at Samsun Medical Park Hospital Chest Diseases outpatient clinic were evaluated between January 2013 and April 2016, and a total of 235 patients were included in this study. Mean age of the patients was 55.3±14.5 (15–88) years, and the male/female ratio was 45/190. The baseline pulmonary function test results of the patients were as follows: mean forced vital capacity (FVC) values 2,825±1,108 (710–6,870) mL and 74.3±22.4 (24–155)%, forced expiratory volume in 1 second (FEV 1) values 1,789±774 (480–4,810) mL and 58.1±20.0 (20–130)%, FEV 1/FVC values 62.5±6.8 (39–70)%. Reversibility criteria following bronchodilator treatment were present in 107 (45.5%) patients. We specified five subgroups for patients according to their clinical, radiological, and pulmonary test findings, namely Group 1 (asthma), Group 2 (ACOS), Group 3 (chronic bronchitis), and Group 4 (emphysema). Additionally, a group of patients who had clinical and spirometric features of both asthma and chronic bronchitis in association with underlying emphysema (emphysema with chronic bronchitis and emphysema with asthma) was defined as the undifferentiated obstruction (UNDO) group. Number and percentage distribution of patients by groups were 58 (24.7%) in the asthma group, 70 (29.8%) in the ACOS group, 61 (26%) in the chronic bronchitis group, 32 (13.6%) in the emphysema group, and 14 (6%) in the UNDO group. In conclusion, in our study, the types of obstructive airway diseases could be classified based on clinical, radiological, and pulmonary function test findings into five groups, including asthma, ACOS, chronic bronchitis, emphysema, and both asthma and chronic bronchitis in association with underlying emphysema (emphysema with chronic bronchitis and emphysema with asthma) or the so-called undifferentiated obstruction. We suggest that these patient groups can be determined more accurately by studies that evaluate the association between spirometric FEV 1, FEV 1/FVC values, and reversibility ratios.