Aim The aim of the present study was to assess the occurrence and determinants of poor adherence to pharmacological treatment in a cohort of primary care patients with chronic obstructive pulmonary disease (COPD), paying special attention to the role of age, comorbidity and polypharmacy. Methods We identified a cohort of COPD patients using the primary care Italian Health Search – IMS Longitudinal Patient Database. We assessed 1‐year adherence to COPD maintenance pharmacotherapy (encompassing inhaled corticosteroids, long‐acting beta agonists and long‐acting anticholinergics). Poor adherence was defined as <80% of proportion of days covered by pharmacological treatment over a 1‐year period. Results Of 22 505 patients (mean age 67.3 ± 13.2; 41.3% women) entering the study, 17 486 (77.7%) were poorly adherent. According to multivariate analysis, poor adherence is less likely in older adults (OR 0.51, 95% CI 0.40–0.66), in non‐smokers (OR 0.77, 95% CI 0.69–0.86) and in those with a history of alcohol abuse (OR 0.74, 95% CI 0.58–0.94). Higher comorbidity (OR 1.43, 95% CI 1.13–1.80) was positively associated with poor adherence. Polypharmacy was associated with poor adherence only in patients aged ≥65 years (OR 1.34, 95% CI 1.13–1.59). Finally, COPD severity was associated with a reduced likelihood of poor adherence (OR 0.20, 95% CI 0.07–0.61 for stage IV). Conclusions The present findings show that poor medication adherence is common in patients with COPD receiving long‐term treatment. The interaction between age and polypharmacy, and the role of comorbidity suggest a pivotal role of biological age as a steering determinant of poor adherence. Geriatr Gerontol Int 2017; ••: ••–••.