OBJECTIVE: To examine the degree of association between medical conditions and work-loss and to estimate the costs associated with work absenteeism among workers in US during 2001. METHODS: Data were extracted from the 2001 Medical Expenditure Panel Survey, a nationally representative survey of medical care use and expenditures conducted by the Agency for Healthcare Research and Quality. The study sample included heads of household, 23-65 years old, who were employed for the entire year (not self employed). Of interest was the incidence of work loss during 2001. Additional information was collected on number of work days lost during the year, the associated medical conditions based on ICD-9-CM codes and other demographic and employment characteristics. Logistic regression was used to assess association of medical conditions with work absenteeism controlling for other characteristics. RESULTS: In total, 4687 persons were identified. Mean age was 40.6 years, 54.4% were male, 18.8% were non-white, and 51.2% had at least high-school education. Workers earned on average $16.8 per-hour, and worked 41.5 hours-per-week. Work loss was reported by 2614 persons (55.8%), who on the average lost 8.5 work-days per year (median 3.3 days), valued at $1069 based on reported hourly wages (median $365). After adjusting for other demographic and employment characteristics, logistic regression analysis revealed that medical conditions were significant predictors of absenteeism. Specifically (odds ratio; 95% confidence intervals): infectious diseases (5.0; 4.1-6.2), mental disorders (1.6; 1.3-2.0), respiratory system (3.3; 2.9-3.8), digestive system (2.5; 2.0-3.1), and musculoskeletal system (1.8; 1.6-2.2). Absenteeism was more likely to be reported among females (1.4; 1.3-1.7) and those with sick benefits (1.3; 1.1-1.5). CONCLUSION: Medical conditions are significant predictors of work loss and associated costs. To reduce incidence and costs associated with work loss, effective policies would need to address the use of effective disease prevention measures and chronic disease treatments.