STUDY OBJECTIVE: Identify risk factors for work disability among adults with asthma treated by pulmonary and allergy specialists. DESIGN: Cross-sectional survey, including retrospective work history data. PARTICIPANTS: Sixty-eight pulmonary and 16 allergy internal medicine subspecialists maintaining a registry of patient visits for asthma; 698 registered patients aged 18 to 50 years, of whom 601 (86%) were studied. MEASURES: Computer-assisted, telephone-administered structured interview assessing asthma severity, perceived general health status, asthma quality of life, demographics, and work history. Complete work disability defined as total work cessation attributed to asthma; partial work disability defined as change in job, duties, or reduction in work hours attributed to asthma. RESULTS: Complete cessation of work due to asthma was reported by 40 (7%; 95% confidence interval [CI], 5 to 9%) and partial work disability by 53 (10%; 95% CI, 7 to 12%) of 550 subjects with a history of labor force participation. Severity of asthma score predicted both complete disability (odds ratio [OR], 7.9; 95% CI, 4.2 to 15 per 10-point increment) and partial disability (OR 2.6; 95% CI, 1.6 to 4.2). Taking illness severity into account, job conditions, occupation, and work exertion carried a combined disability OR of 3.9 (95% CI, 1.7 to 8.6). CONCLUSIONS: Work disability is common among adults with asthma receiving specialist care. Severity of disease is a powerful predictor, but not the sole predictor of disability in this group. Working conditions, including job-related exposures, are associated with added disability risk even after taking illness severity into account.