We report the first large-scale outbreak of echovirus 19 infection. It occurred in the north-east of England during the summer and autumn of 1974. The virus was isolated from 268 patients in the region. The infection spread from the urban to more rural areas, reaching a peak in mid-August. Males were affected more often than females in the ratio 1·6:1. Half of the patients were under eight years of age, relatively few were over 35 years. Aseptic meningitis and upper respiratory infections were the commonest presentations, though a wide range of other diseases occurred including gastroenteritis, myalgia, pericarditis, undifferentiated pyrexia, rashes and a syndrome analagous to bacteraemic shock. There was no evidence that the pattern or severity of the disease changed during the outbreak. Infants under the age of six months were more seriously affected than older children and adults. All patients except one made an uneventful recovery. Of the routine tissue culture cells HEp2 and HeLa were by far the most satisfactory for virus isolation.