MediFair Act of 2003 - Amends title XVIII (Medicare) of the Social Security Act (SSA) to direct the Secretary of Health and Human Services to establish a system for making adjustments to the amount of payment made to entities and individuals for items and services provided under the original Medicare fee-for-service program under parts A (Hospital Insurance) and B (Supplementary Medical Insurance). Requires the Medicare Payment Advisory Commission (MEDPAC) to develop recommendations on policies and practices that would encourage: (1) healthy outcomes and quality care under the Medicare program in States with respect to which payments are reduced under such system; and (2) the efficient use of payments made under the Medicare program in such States.