In this population-based study of asthma in the State of Maine, the authors investigated how often asthma symptoms were exacerbated in the workplace. Participants from 5 hospital service areas in Maine completed a telephone questionnaire. Of 474 adult participants (18-65 yr of age) employed during the preceding year and for whom information on occupation and industry was available, 64 (13.5%) were identified with current asthma, including 28 (5.9%) with current physician-diagnosed asthma and 36 (7.6%) who met criteria for symptoms consistent with asthma. Jobs were identified a priori as "high-risk" or "low-risk" for asthma. Of the 64 asthma cases, 16 (25%) reported that their coughing or wheezing worsened at work. Among the symptom-based cases, the percentage with workplace exacerbation of asthma was elevated for high-risk jobs (7/14 = 50%) vs. low-risk jobs (3/22 = 13.6%) (p = 0.03). No similar elevation was observed for individuals with current physician-diagnosed asthma, which might have resulted, in part, from a healthy worker effect.