Background. Benefits associated with probiotic administration to children seeking emergency department care with diarrheal disease are unknown. Methods. In this 3-site, double-blind, placebo-controlled study, children aged 4 to 48 months with gastroenteritis were randomized to receive 5 days of placebo, low-dose (4 × 109 colony forming units per day), or high-dose (8 × 109 colony forming units per day) probiotic ( Lactobacillus helveticus and Lactobacillus rhamnosus) in a 2:1:1 ratio. The primary outcome was day care absenteeism. Results. The proportion of children missing a day of day care was 63% (39/62) and 61% (37/61) in the placebo and probiotic arms, respectively (95%CI −14.6% to 18.9%). The proportions experiencing unscheduled health care provider visits and intravenous fluid rehydration were 24% (15/62), 7% (4/62), and 30% (18/61), 5% (3/61) in the placebo and probiotic study arms, respectively ( P = .52 and P = .65). None of the results differed based on probiotic dose. Conclusions. The probiotic evaluated did not reduce absenteeism. Since power was suboptimal, further evaluation is required.