Asthma and chronic obstructive pulmonary disease (COPD) are both characterized by the presence of airflow obstruction. Both diseases are not rare in the elderly population. Distinguishing between these diseases is difficult and may be impossible in some older patients. The aim of the study was to investigate clinical and functional characteristics and the presence of atopic status in elderly subjects compared to COPD patients. Fifty-one patients over 60 years of age were selected for the study (27 patients with late-onset asthma, 24 patients with COPD). Atopy was defined by skin prick test and serum total IgE concentrations which were measured in all patients. Pulmonary function tests including airflow rates, lung volumes, airway resistance, diffusing capacity, and arterial blood gases analysis were performed in all patients. The rate of skin prick test positivity in asthmatics was significantly higher than that of the COPD patients. FEV1 was lower in COPD patients than in asthmatic patients. Bronchial reversibility in asthmatics became significantly higher than in COPD patients. While FRC and RV were increased in both groups showing same degree of pulmonary hyperinflation, patients with COPD demonstrated significantly decreased DLCO when compared to asthmatic patients. The level of both PO2 and PCO2 in patients with COPD significantly differed from asthmatics. In conclusion, a history of heavy smoking, decreased diffusing capacity for carbon monoxide, the presence of more prominent lung hyperinflation and chronic hypoxemia favour the diagnosis of COPD, whereas atopy and significant bronchodilator responsiveness favour the diagnosis of asthma.