Access to health care is often challenging, even prohibitive, to people with disabilities. A burgeoning elderly population is adding to this disserved public. Inaccessible medical instrumentation is a fundamental barrier to health care employees and consumers with disabilities. The Rehabilitation Engineering Research Center on Accessible Medical Instrumentation (RERC-AMI) is designing Medical Equipment and Device Accessibility and Universal Design Information Tool (MED-AUDIT) to assess the usability of medical instrumentation for people with disabilities. As part of this process, the measurement parameters of an impairment categorization scheme (consistent conceptual definitions, mutually exclusive, comprehensive) are discussed and will provide a dimension to MED-AUDIT. Examples of existing impairment-related categorization schemes, formed for a variety of purposes, are reviewed and the measurement parameters for the MED-AUDIT impairment categorization scheme are discussed. Finally, a tentative RERC-AMI MED-AUDIT impairment categorization scheme is presented.