In a ten-year period at the Occupational and Environmental Medicine Program (OEMP) of the University of Washington in Seattle, 71 patients were determined by attending physicians to have work-related asthma. In this cross-sectional descriptive study, we describe these patients. Data were obtained from a database maintained by the OEMP and from chart reviews. We found that the three most common specific agents causing asthma were isocyanates, red cedar, and crabs. At least one pulmonary function study was available for all patients and was positive in 56 patients (79%). Among the 71 asthma cases reported in this article, 18 (25%) were attributed to reactive airways dysfunction syndrome (RADS); 19 (27%) to exacerbation of pre-existing asthma; 27 (38%) to sensitization; and 7 (10%) had undetermined causes. We conclude that occupational asthma presents as a result of diverse exposures in multiple work settings and with an array of characteristics. Prevention efforts need to recognize this diversity.