Most health and work productivity studies have focused on individual conditions without considering comorbidity. We illustrate the implication of this neglect by examining the effects of comorbid mental disorders on role impairment (number of sickness absence and work cut-back days in the past month) among people with chronic physical disorders. A nationally representative household survey of 5877 respondents assessed current mental and physical disorders and role impairments. Four physical disorders were sufficiently common to be studied: hypertension, arthritis, asthma, and ulcers. All 4 physical disorders were associated with significant role impairments in bivariate analyses. However, further analysis showed that these impairments were almost entirely confined to cases with comorbid mental disorders. Effectiveness trials in workplace samples are needed to evaluate the cost-effectiveness of treating comorbid mental disorders among workers with chronic physical disorders.