From 1972 to 1982, approximately 1,500-2,100 US Air Force Reserve personnel trained and worked on C-123 aircraft that had formerly been used to spray herbicides in Vietnam as part of Operation Ranch Hand. After becoming aware that some of the aircraft on which they had worked had previously served this purpose, some of these AF Reservists applied to the US Department of Veterans Affairs (VA) for compensatory coverage under the Agent Orange Act of 1991. The Act provides health care and disability coverage for health conditions that have been deemed presumptively service-related for herbicide exposure during the Vietnam War. The VA denied the applications on the basis that these veterans were ineligible because as non-Vietnam-era veterans or as Vietnam-era veterans without "boots on the ground" service in Vietnam, they were not covered. However, with the knowledge that some air and wipe samples taken between 1979 and 2009 from some of the C-123s used in Operation Ranch Hand showed the presence of agent orange residues, representatives of the C-123 Veterans Association began a concerted effort to reverse VA's position and obtain coverage. At the request of the VA, Post-Vietnam Dioxin Exposure in Agent Orange-Contaminated C-123 Aircraft evaluates whether or not service in these C-123s could have plausibly resulted in exposures detrimental to the health of these Air Force Reservists. The Institute of Medicine assembled an expert committee to address this question qualitatively, but in a scientific and evidence-based fashion. This report evaluates the reliability of the available information for establishing exposure and addresses and places in context whether any documented residues represent potentially harmful exposure by characterizing the amounts available and the degree to which absorption might be expected. Post-Vietnam Dioxin Exposure rejects the idea that the dioxin residues detected on interior surfaces of the C-123s were immobile and effectively inaccessible to the Reservists as a source of exposure. Accordingly, this report states with confidence that the Air Force Reservists were exposed when working in the Operation Ranch Hand C-123s and so experienced some increase in their risk of a variety of adverse responses.