In September 2017 Colorado public health officials investigated an outbreak of gastroenteritis of unknown etiology among patrons who ate a restaurant located in Littleton, Colorado. Four people reported diarrhea. The implicated meal date was September 2, 2017. The median incubation period was 2.5 hours (range, 2 to 3 hours). The median duration of illness was 14.5 hours (range, 2 to 36 hours.) No one was hospitalized and no one died.