Chronic obstructive pulmonary disease (COPD) is an increasing cause of morbidity and mortality worldwide, and it has been strongly correlated to tobacco smoking. While a number of studies have concentrated on smokers only, recent published data demonstrate that at least one fourth of patients with COPD are non-smokers, and that the burden of COPD in non-smokers is also higher than previously believed. Risk factors of COPD in non-smokers may include genetic factors, long-standing asthma, outdoor air pollution (from traffic and other sources), environmental smoke exposure (ETS), biomass smoke, occupational exposure, diet, recurrent respiratory infection in early childhood, tuberculosis and so on. In Asian region, indoor/outdoor air pollution and poor socioeconomic status may play important roles in the pathogenesis of non-smoking-related COPD. The prevalence of COPD among never smokers varies widely across nations. Such a variation may arise from several aspects, including study design, definition of COPD, diagnostic criteria, age and gender distribution of the studied population, local risk factors and socioeconomic status. More investigations and efforts are required to elucidate the involved factors and their shared contributions to non-smoking-related COPD so as to achieve better estimation and reduction of the burden of this neglected entity worldwide.