OBJECTIVES: U.S. studies using varying methodologies have reported different estimates for the indirect cost per person with IBD. Our analysis contributes to this literature, by using the 1999 sample of the National Health Interview Survey (NHIS) to estimate the employment effect of Inflammatory Bowel Disease (IBD) in the United States. METHODS: Our predictive analysis adapts the theory of labor supply to a health context. A weighted logistic regression model was used to estimate the odds ratio (OR) of being out of the labor force as determined by predictive variables including having been diagnosed with IBD, with or without symptoms. Controls included demographic variables and health status indicators. For those people in the labor force, a second analysis was performed to determine whether an individual worked throughout the entire duration of the past 12 months or less than 12 months. SUDAAN 8.0 was used to generate population estimates, systematically correcting for survey design. RESULTS: 31.5% of IBD patients who had experienced symptoms in the past 12 months reported being out of the labor force with OR=2.07. We estimated the excess in the non-participation rate attributable to IBD with symptoms in the past 12 months in the United States to be 11.7%. Based on this, the indirect cost of non-participation attributable to IBD in 1998 was $3.5 billion US dollars or $4973 per person with IBD and symptoms. According to the second weighted logistic regression, having IBD had no association with the duration of work, for those who are in the labor force. Consequently, the indirect cost of IBD reported can be interpreted as the indirect cost of IBD associated with employment losses. CONCLUSIONS: By using directly observed data in our analysis, this method of estimation can be used to predict the overall paid-employment burden of IBD.