The Department of Veterans Affairs (VA) is issuing this interim final rule to amend its adjudication regulations regarding compensation for disabilities resulting from undiagnosed illnesses suffered by veterans who served in the Persian Gulf War. This amendment is necessary to extend the presumptive period for qualifying chronic disabilities resulting from undiagnosed illnesses that must become manifest to a compensable degree in order that entitlement for compensation be established. The intended effect of this amendment is to provide consistency in VA adjudication policy and preserve certain rights afforded to Persian Gulf War veterans and ensure fairness for current and future Persian Gulf War veterans.