Most Americans gain entry into the medical care system through office-based primary care physicians. The Medicaid program was created in 1965 in part to increase the access of low-income people to medical services in that mainstream. But, over the years, office-based physicians have reduced their treatment of Medicaid patients, and many have withdrawn from the program altogether. The result is not only that the original programmatic goal has not been fully achieved, but also that the costs of the program are higher than they would be otherwise. In this article, the importance of Medicaid participation by office-based primary care physicians is described, and a number of obstacles to their participation are identified. The obstacles include state policies regarding eligibility, coverage, and provider compensation. The article recommends actions pertaining to these policies that might increase participation.