At the end of 1979, Vietnam veterans in Australia claimed that the rate of congenital anomalies in their children was high, attributing this to their exposure in Vietnam to the defoliant Agent Orange. The present study was undertaken to determine whether the risk of fathering a child with an anomaly was greater for Vietnam veterans than for other men, including contemporary members of the Australian Army who did not serve in Vietnam.Case infants were those with anomalies diagnosed at, or shortly after, birth. Controls were live-bom babies with out diagnosed anomalies and were individually matched to case infants by hospital, period of birth, age of mother, and (where feasible) hospital payment category. Each father's surname and initials were compared with those of every member of the Australian Army who served at any time between 1962 and 1972, the period of Australian involvement in Vietnam. The data were analyzed by means of conditional logistic regression. This technique allows a fully matched analysis which takes into account several potentially confounding variables.