Congress needs to reform Medicare and Medicaid to improve the programs’ integrity and sustainability, the comptroller of the Government Accountability Office, is urging congressional leaders in a letter.

Because of Medicare’s size and complexity, it is “vulnerable to improper payments and inefficient payment systems,” David Walker said. Meanwhile, Medicaid is at risk of “increased and inappropriate federal spending,” he added.

Congress should assess the Centers for Medicare & Medicaid Services’ managerial oversight of the programs, Walker said. He also recommends that Congress reform Medicaid to prevent states from inappropriately obtaining matching funds.