As the classic mineral dust-induced pneumoconioses decrease in frequency because of the control of exposure, obstructive airway diseases have emerged as the most prevalent category of occupational respiratory disorder. Unlike the pneumoconioses, recognition of work-relatedness for asthma and chronic obstructive pulmonary disease (COPD) is difficult. This is the case for two reasons. First, these are multifactorial diseases that are strongly associated with nonoccupational exposures. Second, the occupational dose-response and temporal relationships for obstructive airway diseases are complex. Nonetheless, because asthma and COPD are common diseases in the general population, even a small increase in the percentage of prevalence due to occupational exposures would have major public health impact and should be preventable. The purpose of this statement is to reveiw the evidence implicating occupational factors in the pathogenesis of obstructive airway diseases and to quantify the controbution of work-related risk to the burden of these diseases in the general population. Assessing the occupational component of the total burden of asthma and COPD can better inform preventive strategies designed to reduce the orbidity and mortality associated with these conditions.