Reinstatement of the Medicare Rehabilitation Benefit Act of 1998 - Amends title XVIII (Medicare) of the Social Security Act to repeal the financial limitation on rehabilitation services under part B (Supplementary Medical Insurance) of the Medicare program.

Provides that for outpatient physical therapy services, outpatient occupational therapy services, and outpatient speech-language pathology services covered under Medicare and furnished on or after January 1, 2000, the Secretary of Health and Human Services shall implement a new payment methodology based on the classification of individuals by diagnostic category, functional status, and prior use of services in both inpatient and outpatient settings. Requires that such payment methodology be designed so that, taking into account the increased expenditures resulting from this Act, it does not result in any increase or decrease in the expenditures under Medicare on a fiscal year basis.