The gastrointestinal flora plays a complex and important role in the development of healthy immunologic and digestive function in children. Probiotics are safe in healthy children and effective in reducing the risk of antibiotic-associated diarrhea and the duration of acute infectious diarrhea. Probiotics may also be effective in preventing community-acquired diarrheal infections, in reducing the risk of necrotizing enterocolitis in premature infants, and in the prevention and treatment of atopic dermatitis. The exact strain or combination of strains most effective for common clinical indications has yet to be determined, but the exact strain used seems less important than whether an adequate dose is used (typically 5 to 10 billion CFUs per day or higher). Clinicians should familiarize themselves with the products available because there is a wide range in their quality.