The overall prevalence of asthma symptoms and/or immunologic sensitization to TDI was low among workers that completed their first year of employment at this modern TDI polyurethane production facility. However, 14.2% of the original workers developed findings suggestive of possible TDI-related health effects (new asthma symptoms, TDI- specific IgG, new airflow obstruction, and/or a decline in FEV1 ≥ 15%). These findings should be considered in the context of available diagnostic tests for isocyanate sensitization and asthma, as well as uncertainty regarding the natural history of disease. There is no widely available diagnostic test to confirm isocyanate asthma and the time to onset can be highly variable. While isocyanate asthma has been reported to occur within weeks to months of exposure, the latency period between onset of exposure, immune sensitization, and asthma symptoms may vary and has been difficult to define [Malo, et al. 1992, Ott, et al. 2000, Petsonk, et al. 2000, Tarlo and Liss 2002]. With continuing improvements in industrial hygiene and reduction of airborne TDI levels, the latency period, may be further increased. Long-term follow-up of the current cohort, while challenging, is needed, as well as further evaluation of those with findings suggestive of possible isocyanate asthma, to better understand the risks of isocyanate exposures, and to assess whether current work controls are effective at preventing isocyanate sensitization and asthma.