An outbreak of gastroenteritis occurred among persons who attended a party at a private residence in Livingston county, New York. Food for the event was provided by a local convenience store. Plesiomonas shigelloides and Salmonella Hartford were isolated in stool specimens. Nine specimens yielded only Plesiomonas shigelloides, three only Salmonella Hartford, and two specimens yielded both Plesiomonas shigelloides and Salmonella Hartford. Illness appeared to be associated with eating potato salad, macaroni salad, and ziti. Salmonella Hartford was isolated from the macaroni salad and ziti. Salmonella Hartford and Plesiomonas shigelloides was isolated from the potato salad. Escherichia coli was isolated from the water at the convenience store. Water samples collected from the well that supplied the convenience store with water yielded Salmonella Hartford and Plesiomonas shigelloides. Store foodhandlers denied having any illness symptoms prior to making the food for the party, but three food handlers reported being ill in the days after the party occurred. All three had eaten foods prepared for the party. Plesiomonas shigelloides was recovered from the stool of these food workers. The inspection of the market revealed many sanitary violations. The water for the store was an unprotected dug well; the well was fed with shallow ground water. Runoff from adjacent farms could have contaminated the water. The chlorinator for the system was improperly maintained. The food was likely contaminated by the water during preparation.