This study was conducted to investigate the cause and magnitude of food poisoning among residents and visitors for a birthday party in a rural area of Kyongju city in september, 1996. The total subjects were 137 persons, 119 residents(53 males, 66 females), including 7 hospitalixed patients and 18 visitors(8 males, 10 females). The investigation consisted of an interview survey, a study on clinical characteristics for the patients hospitalized, bacteriological examinations of the underground water and microbiologic examinations on microbes isolated from the patients. The population at risk was 59 persons(24 males, 35 females). The attack rate was 50.0%(12 cases) for males, 48.6% for females(17 cases). The cases were distributed evenly for all age groups. The attack rates for each party-food and possible fooe groups were not significantly different. Most clinical symptoms were significantly more frequent among cases than non-ases: abdominal pain(73.1%), diarrhea(73.1%), chilliness(69.2%), fever(65.4%), anorexia(61.5%), nausea(53.8%), general weakness(50.0%) and dizziness(50.0%) were the major symptoms among the cases. The admission rate among the cases was 24.1%(1 male, 6 females). In the stool cultures, Salmonella species group D was isolated from 6 persons of 85 examinees. It was identified as Salmonella enteritidis by serological diagnosis. The samples of underground water were assessed Enon-compatible for drinking in 10 wells(83.3%) of this rural area and it was suggested that it could have been contaminated from cattle feces. There were two wells in the party house, one of them was contaminated by bacterias including E. coli. The contaminated water was stored in a water tank located on the rooftop. This water was used for dish washing and cooking. Wd concluded that the cause of this epidemic was the underground water contaminated by Salmonella enteritidis from guman carriers or domestic animal carriers.