An outbreak of acute enteritis due to Campylobacter fetus subspecies jejuni involving a total of 35 out of 74 children occurred at a nursery school of Tokyo in January 1979 and lasted for 7 days. It was the first case of a community outbreak of the disease to be recognized in Japan. The major symptoms observed in the patients consisted of diarrhea (88%), fever (82%), abdominal pain (39%), and vomiting (6.1%). The rate of isolation of the organism from the patients was 39%. Sera of four patients showed elevated agglutinin titers against the organism ranging from 1:80 to 1:320. Although it is suggested that the outbreak was caused by a communal lunch or between-meal snacks prepared by and provided at the nursery school, the incriminated food, source and route of contamination could not be pinpointed.