Some patients with chronic obstructive pulmonary disease (COPD) are never-smokers, which suggests that there must be other important risk factors. This paper describes the evidence for an association between occupational exposure and COPD. In several studies a consistent and predominantly significant association between occupational exposures and COPD is found, even though the studies vary in design, enrolled populations and in measures of exposure and outcome. Strong evidence supports a causal association between multiple categories of occupational exposure and COPD, both within and across industry groups.