Despite increases in Medicaid payment rates and enrollment, the proportion of U.S. physicians accepting Medicaid patients has decreased slightly over the past decade, according to a national study by the Center for Studying Health System Change (HSC). In 2004-05, 14.6 percent of physicians reported that they received no revenue from Medicaid, an increase from 12.9 percent in 1996-97. There were also small increases in the percentage of physicians who were not accepting new Medicaid patients. A more striking trend is that care of Medicaid patients is becoming increasingly concentrated among a smaller proportion of physicians who tend to practice in large groups, hospitals, academic medical centers and community health centers. Relatively low payment rates and high administrative costs are likely contributing to decreased involvement with Medicaid among physicians in solo and small group practices.