Although diisocyanates are known to cause asthma in the workplace, the incidence of diisocyanate-related asthma has been decreasing. Diisocyanates do not rank as one of the top 10 leading causes of occupational asthma. Recent data show a consistent picture of a decline in asthma rates associated with diisocyanates over the last decade. Reduction in diisocyanate-related occupational asthma is primarily due to industry product stewardship activities, including education and training, enhanced worker awareness, and improved work practices.