Serum dioxin studies of Vietnam (VN) veterans, military historical records of tactical herbicide use in Vietnam, and the compelling evidence of the photodegradation of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and other aspects of environmental fate and low bioavailability of TCDD are consistent with few, if any, ground troop veterans being exposed to Agent Orange. That conclusion, however, is contrary to the presumption by the Department of Veterans Affairs (DVA) that military service in Vietnam anytime from January 9, 1962 to May 7, 1975 is a proxy for exposure to Agent Orange. The DVA assumption is inconsistent with the scientific principles governing determinations of disease causation. The DVA has nonetheless awarded Agent Orange-related benefits and compensation to an increasing number of VN veterans based on the presumption of exposure and the published findings of the Institute of Medicine that there is sufficient evidence of a "statistical association" (a less stringent standard than "causal relationship") between exposure to tactical herbicides or TCDD and 15 different human diseases. A fairer and more valid approach for VN veterans would have been to enact a program of "Vietnam experience" benefits for those seriously ill, rather than benefits based on the dubious premise of injuries caused by Agent Orange.