Antibiotic-associated diarrhea (AAD) is the most common adverse effect of antibiotic therapy. Our aim was to determine the effectiveness of a dietary supplement of yogurt for prevention of AAD. Two hundred two hospitalized patients receiving oral or intravenous antibiotics were randomized to receive or not receive a dietary yogurt supplement, consisting of 227 grams of commercial yogurt, and followed for 8 days. Mean age of the study group was 70 years and 43% were male. Compliance and 8-day follow-up were 85% and 91%, respectively. Patients receiving yogurt reported less frequent diarrhea (12% vs 24%; P = 0.04), and significantly less total diarrhea] days (23 vs 60). The cumulative proportions of patients without diarrhea were significantly different (P = 0.02) between patients receiving and not receiving yogurt. For conclusion, dietary supplementation with yogurt is a simple, effective, and safe treatment that decreases the incidence and duration of AAD.