Methods. Estimates of direct medical expenditures and indirect costs (in 1985 dollars) were derived from data available from the National Center for Health Statistics. These cost estimates were projected to 1990 dollars.

Results. The cost of illness related to asthma in 1990 was estimated to be $6.2 billion. Inpatient hospital services represented the largest single direct medical expenditure for this chronic condition, approaching $1.6 billion. The value of reduced productivity due to loss of school days represented the largest single indirect cost, approaching $1 billion in 1990. Although asthma is often considered to be a mild chronic illness treatable with ambulatory care, we found that 43 percent of its economic impact was associated with emergency room use, hospitalization, and death. Nearly two thirds of the visits for ambulatory care were to physicians in three primary care specialties - pediatrics, family medicine or general practice, and internal medicine.

Conclusions. Potential reductions in the costs related to asthma in the United States may be identified through a closer examination of the effectiveness of care associated with each category of cost. Future health policy efforts to improve the effectiveness of primary care interventions for asthma in the ambulatory setting may reduce the costs of this common illness.