A recent change will benefit veterans suffering from undiagnosed illnesses and medically unexplained chronic multi-system illnesses following service in the Southwest Asia Theater of Operations during the Persian Gulf War. Manifestations of an undiagnosed illness may include fatigue, unexplained dermatological signs, headache, muscle pain, joint pain, neurological signs and symptoms, neuropsychological signs or symptoms, signs or symptoms involving the upper or lower respiratory system, sleep disturbances, gastrointestinal signs or symptoms, cardiovascular signs or symptoms, abnormal weight loss, and menstrual disorders. To qualify for service connections, a veteran's disability must manifest during the presumptive period. In an interim final rule effective December 29, 2011, the VA extended the statutory period for compensation from December 31, 2011, to December 31, 2016. This extension is invaluable for veterans whose symptoms have not yet manifested or whose symptoms may worsen to a compensable degree during this time frame.