In 2005 Medicare paid over $1.4 billion for anesthesia services. These services are generally provided by anesthesia practitioners, such as anesthesiologists and certified registered nurse anesthetists (CRNAs). A government-sponsored study found that Medicare payments for anesthesia services are lower than private payments. Congress is concerned that this difference may create regional discrepancies in the supply of anesthesia practitioners, and asked GAO to explore this issue. GAO examined (1) the extent to which Medicare payments for anesthesia services were lower than private payments across Medicare payment localities in 2004, (2) whether the supply of anesthesia practitioners across Medicare payment localities in 2004 was related to the differences between Medicare and private payments for anesthesia services or the concentration of Medicare beneficiaries, and (3) compensation levels for anesthesia practitioners in 2005 and trends in graduate training. GAO used claims data from two anesthesia service billing companies that bill private insurance payers and Medicare to calculate payments by payer for seven anesthesia services in 41 Medicare payment localities. GAO also used data from the Centers for Medicare & Medicaid Services (CMS) and other sources to determine practitioner supply and Medicare beneficiary concentration in 87 Medicare payment localities.