An outbreak of infections caused by enterovirus 71 occurred in southeastern Australia during the winter of 1986. Infection was confirmed by virus isolation or serology in 114 patients, 65 of whom were admitted to hospital. Fifty-one percent of inpatients were infants younger than 12 months old and 85% were younger than 5 years old. Many cases of hand, foot and mouth disease occurred in the community during the epidemic, but 51% (33 of 65) of patients admitted to hospital had central nervous system involvement, often associated with severe symptoms. Six patients had encephalitis and one had a poliomyelitis-like paralytic illness. Various skin manifestations other than hand, foot and mouth disease occurred, especially in young children, and 25 patients had significant respiratory disease including at least 7 with pneumonia. Enterovirus 71 is one of very few viruses that cause hand, foot and mouth disease as well as a variety of other clinical manifestations. The most important of these is meningoencephalitis, which causes significant morbidity, especially in infants and young children.