Antibiotic-associated diarrhea (AAD) occurs in approximately 25% of patients receiving antibiotics. Hospitalized patients with AAD are at increased risk for nosocomial infections and have a higher mortality. Probiotics are living microorganisms used to restore gut health by changing the intestinal microbiota. Several have been studied for the prevention of AAD. Five meta-analyses of trials of probiotics for the prevention of AAD have been performed. The results showed an overall reduction in the risk of AAD when probiotics were coadministered with antibiotics. McFarland conducted the largest meta-analysis to date analyzing 25 randomized controlled trials of probiotics for the prevention of AAD including 2810 subjects. More than half of the trials demonstrated efficacy of the probiotic. In particular, Lactobacillus GG, Saccharomyces boulardii, and the probiotic mixtures were effective. The Cochrane Database of Systematic Reviews published a review of the literature on the use of probiotics for the prevention of pediatric AAD, including 10 randomized trials testing 1986 children. The per protocol pooled analysis, but not the intent-to-treat analysis, showed that probiotics are effective for preventing AAD with the number needed to treat to prevent 1 case of diarrhea being 10. Lactobacillus GG, Bacillus coagulans, and S. boulardii appeared to be most effective. Probiotics are generally safe, however, they should be used with caution in patients who have compromise of either the immune system or the integrity of the intestinal mucosa, and in the presence of a central venous catheter.