Work-related asthma (WRA) includes work-exacerbated asthma (preexisting or concurrent asthma worsened by factors related to the workplace environment) and occupational asthma (new onset asthma attributed to the workplace environment). WRA is a preventable occupational lung disease associated with serious adverse health and socioeconomic outcomes. Among workers with similar occupational exposures, WRA diagnosis offers unique opportunities for prevention. The American Thoracic Society estimated that 15% of U.S. adults with asthma have asthma attributable to occupational factors. State-level information on the proportion of asthma that is WRA is limited but could be useful to prioritize and guide investigations and interventions. To estimate current asthma prevalence and the proportion of asthma that is WRA, CDC analyzed data from the 2006-2009 Behavioral Risk Factor Surveillance System (BRFSS) from 38 states and the District of Columbia (DC). This report summarizes the results of that analysis, which indicated that among ever-employed adults with current asthma, the overall proportion of current asthma that is WRA was 9.0%. State-specific proportions of asthma that are WRA ranged from 4.8% to 14.1%. Proportions of WRA were highest among persons aged 45-64 years (12.7%), blacks (12.5%), and persons of other races (11.8%). These findings provide a baseline that state and national health agencies can use to monitor the proportion of WRA among persons with current asthma. Enhancing WRA surveillance through routine collection of industry and occupation information will greatly increase understanding of WRA.