Non-Homeland Security Mission Performance Act of 2003

Non-Homeland Security Mission Performance Act of 2003 - Requires the Under Secretary of each entity within the Department of Homeland Security that performs non-homeland security functions to report to the Secretary of Homeland Security and specified congressional committees on its performance of such functions, with an emphasis on examining the continuing performance level. Requires new entities that are transferred to the Department and that perform such functions to submit such reports for a five-year period.Directs the Comptroller General to monitor, evaluate, and report to specified congressional committees on the implementation of this Act.Directs the Department, in required annual performance reports, to clarify, describe, and evaluate the performance of homeland and non-homeland security functions.