A critical analysis of the literature shows that only a few viral agents have been proved by accepted criteria to cause acute gastroenteritis. Rotavirus, of the RNA family reoviridae, is the cause of most childhood gastroenteritis. The parvovirus-like agents (Norwalk, Hawaii, MC, and W) are proved agents of epidemic gastroenteritis. There is good evidence that the Marcy, FS, and Niigata agents were the causes of gastroenteritis outbreaks. Thirty percent of all acute gastroenteritis episodes in large investigations are still etiologically unaccounted for. Much work remains to be done on define the pathogenesis and immunology of viral gastroenteritides.