Eating at the church youth group dinner on March 2 was associated with developing giardiasis. The foods served at dinner included tacos (meat, onions, tomatoes, lettuce, cheese, salsa, sour cream, and tortillas), corn, peaches, cupcakes, soft drinks, coffee, and tea. No food samples remained for laboratory testing. Persons who became ill were more likely to have eaten lettuce, salsa, onions, or tomatoes. Water consumption was not specifically associated with illness. The salsa had been purchased commercially. The other foods had been prepared in the church kitchen. The food was prepared by mothers of children in the youth group. The mothers denied illness in advance of the outbreak, however five became ill during the outbreak. The church was served by the municipal water supply. Five potential cross connections in the water system were identified, but the water showed adequate chlorination and no evidence of coliform bacteria. The most likely vehicle of transmission was assessed to be taco ingredients. Although all ate the commercially prepared salsa, salsa was unlikely to have transmitted Giardia cysts because the cysts would not remain viable after the pasteurization and canning processes. Two explanations for the contamination were possible. First, if the water was contaminated, the lettuce and tomatoes could have been contaminated when washed. Because the lettuce, tomatoes, and onions were all cut on the same board, cross-contamination could have occurred. Second, if the mother who prepared the lettuce and tomatoes was infected and excreting Giardia cysts, she could have contaminated the vegetables during preparation. However, this mode is less likely because she developed diarrhea 10 days after the meal.