Human factors engineering and system design are critical elements in the newly developing field of telerehabilitation. Telerehabilitation is the remote delivery of rehabilitative services such as monitoring, training, and long-term care of persons with disabilities using telecommunications technology. This paper describes projects at the Rehabilitation Engineering Research Center (RERC) on Telerehabilitation in the context of three conceptual models: telecounseling and training, telemonitoring and assessment, and teletherapy. Issues pertaining to human factors engineering design are identified, and ongoing challenges are discussed.