Aim One of the most significant problems in the treatment of elderly patients is incorrect use of inhaler devices. The purpose of the present study was to assess the parameters affecting treatment adherence among elderly patients. Methods Spirometry, the Mini‐Mental State Examination for cognitive impairment and the Morisky Medication Adherence Scale‐4 were carried out in 121 (88 chronic obstructive lung disease patients according to the Global Initiative for Chronic Obstructive Lung Disease, 33 asthma patients according to The Global Initiative for Asthma (GINA) criteria) participants aged over 65 years. Results The patients with cognitive impairment, low socioeconomic status, a high number of admissions to an emergency service in past year and the presence of dyspnea or sputum had significantly lower inhalation device use scores (P = 0.017, 0.03, 0.025, 0.03 and 0.02). The patients with high Mini‐Mental State Examination scores and forced expiratory volume in 1 s (as liter and percentage) were found to be more successful in using inhaler devices (P = 0.005, 0.007 and 0.022). There was a negative correlation between number of hospitalizations and inhalation device score (P = 0.021).The participants without education/training by a doctor about the inhaler device had a significantly poorer treatment adherence (P < 0.001). Conclusions Older chronic obstructive lung disease and asthmatic patients have more difficulty with the correct use of inhaler devices. Cognitive impairment might be an important parameter that can affect inhalation device technique. Socioeconomic status, smoking, pulmonary symptoms and admissions to hospital were also thought to have effects on the adherence to inhalation therapy. The type of chronic respiratory disease (chronic obstructive lung disease/asthma) is not a major factor influencing therapy adherence. Assessment of cognitive functions, choosing suitable inhalation devices and educational programs for inhaler use could improve the success of inhaler technique in elderly patients. Geriatr Gerontol Int 2017; 17: 999–1005.