The present study aimed to measure physical activity in patients with chronic obstructive pulmonary disease (COPD) to: 1) identify the disease stage at which physical activity becomes limited; 2) investigate the relationship of clinical characteristics with physical activity; 3) evaluate the predictive power of clinical characteristics identifying very inactive patients; and 4) analyse the reliability of physical activity measurements. In total, 163 patients with COPD (Global Initiative for Chronic Obstructive Lung Disease (GOLD) stage I-IV; BODE (body mass index, airway obstruction, dyspnoea, exercise capacity) index score 0-10) and 29 patients with chronic bronchitis (normal spirometry; former GOLD stage 0) wore activity monitors that recorded steps per day, minutes of at least moderate activity, and physical activity levels for 5 days (3 weekdays plus Saturday and Sunday). Compared with patients with chronic bronchitis, steps per day, minutes of at least moderate activity and physical activity levels were reduced from GOLD stage II/BODE score 1, GOLD stage III/BODE score 3/4 and from GOLD stage III/BODE score 1, respectively. Reliability of physical activity measurements improved with the number of measured days and with higher GOLD stages. Moderate relationships were observed between clinical characteristics and physical activity. GOLD stages III and IV best predicted very inactive patients. Physical activity is reduced in patients with chronic obstructive pulmonary disease from Global Initiative for Chronic Obstructive Lung Disease stage II/ body mass index, airway obstruction, dyspnoea, exercise capacity score 1. Clinical characteristics of patients with chronic obstructive pulmonary disease only incompletely reflect their physical activity.