Laboratory testing identified Clostridium perfringens as the cause of the outbreak associated with the Pierre-Mitchell high school boys’ basketball game held in Pierre, South Dakota, on January 31, 2012. The investigation, which included a voluntary questionnaire, implicated the tacos as the source food of the outbreak. Of those who completed the questionnaire, 75% who ate the tacos reported becoming ill. The predominant symptoms were diarrhea and cramps lasting less than 24 hours, although the symptoms in some ill persons lasted longer. Three-quarters of the cases became ill between midnight and 6:00 AM following the game.