Medicare+Choice, the federal program that offers managed care options to Medicare beneficiaries, is struggling for survival following its initial years of rapid growth. In the past three years, dozens of health plans have exited the program; enrollment has shrunk; benefits have deteriorated; cost-sharing requirements have soared; and withdrawals of physicians from the program have disrupted the continuity of patients' care. Mathematica Policy Research has been tracking trends in Medicare+Choice benefits and premiums since the program's inception. This project will continue Mathematica's analysis of these trends for the 2003 and 2004 enrollment years-a critical period that might determine the future of the program and provide lessons for a broader restructuring of Medicare.