An in-depth targeted literature review concentrating on US-based studies was conducted to obtain data on use and costs. British and Canadian studies were also used when data were otherwise unavailable. Data on physician, outpatient, clinic services, dental care,9 prescription medications,9- 11 complementary and alternative therapies,12- 18 behavioral therapies,19- 22 hospital and emergency services,9,23 allied health, equipment and supplies, home health,9 and medically related travel9 were classified as direct medical. Data on child care,9,19 adult care,19- 20 respite and family care,9,19- 20 home and care modifications,9,24 special education,19- 20,25- 27 supported employment,20,28- 34 and other costs9,24 were classified as direct nonmedical. Although some dimensions of care may be misclassified between direct medical and direct nonmedical (for example, many special education programs provide behavioral therapies), because the degree of misclassification is not known, no corrections were made. Costs, as reported in the source materials, were inflated to 2003 US dollars using the all-item consumer price index.35 State-specific costs were transformed to national averages36 and foreign costs were converted to US costs using the latest available Federal Reserve exchange rates.37 Use measures were translated to costs by multiplying the use measures by age group–specific survey-adjusted average costs from the MEPS.6 More in-depth information on how the cost estimates were constructed from these sources is available elsewhere1 and in a technical appendix available on request.