An epizootic occurred among white-tailed deer (Odocoileus virginianus) from July through October 1988 in Missouri (USA). From late July through September, nine necropsied deer had lesions of the peracute or acute forms of hemorrhagic disease (HD) or no apparent lesions, whereas two deer necropsied in October had lesions of the chronic form of HD. Epizootic hemorrhagic disease virus was isolated from two necropsied deer. Based on changes in population indices, there is evidence that deer populations declined in seven of Missouri's 57 deer management units from 1987 to 1990. Based on a deterministic model designed to simulate deer populations in management units, it appeared that summer and fall 1988 mortality ranging from 6% to 16% accounted for the population decreases in deer management units with population declines. Heavily hunted areas where high deer mortality was not reported in the summer and fall of 1988 did not have population declines. Based on these results, we believe that HD mortality was high and resulted in deer population declines in parts of Missouri when combined with hunting harvest.