The Medical Diagnostic Imaging Support (MDIS) System is a four-year contract to install large-scale picture archival and communications systems (PACS) and teleradiology in Army and Air Force medical treatment facilities. MDIS specifications were based on the results of three years of tri-service research and development through the Digital Imaging Network Systems Project and the Tactical Air Command Teleradiology Project. At the time of the government's request for proposals, MDIS functional specifications represented the most comprehensive understanding of the requirements for large-scale PACS and teleradiology complied by a composite team of radiologists, physicists, clinical engineers, hospital administrators, technologists, and computer systems engineers. As MDIS sites become operational, a better understanding of the capabilities and limitations of teleradiology is emerging. This paper reviews functions and subsystems common to all teleradiology systems, MDIS specifications for teleradiology, installation planning, and the status of Army and Air Force Teleradiology with special emphasis on early installations that validate routine teleradiology operations.