An outbreak of infection due to echovirus 4 in Scotland involving 194 cases during 1971-72 is described. Clinical and epidemiological information was obtained and analysed for 181 patients, of whom 149 (82%) developed aseptic meningitis. The majority of cases were older children (39%) and young adults (40%), although the highest attack rate was in infants (10.5 per 100,000 population). An unusual feature of the outbreak was its biphasic nature with cases occurring largely in the same geographic areas in successive years.