Diarrhea that develops in patients after 72 hours of hospitalization is likely to have a nosocomial or iatrogenic etiology. Testing with stool cultures and stool ova and parasites (O&P) is not recommended. Our goal was to reduce this inappropriate testing within a large, urban safety-net hospital system. This was a quality improvement project. We created a best practice advisory (BPA) within the electronic medical record that fires when a stool culture or O&P order is placed 72 hours after admission for any immunocompetent patient. It states that stool testing is low yield and offers the option to remove the order. We measured weekly counts of stool culture and stool O&P orders pre- and postintervention. We also measured the BPA acceptance rate, the 24-hour stool testing reorder rate, and Clostridioides difficile infection rates. Data were analyzed using Welch tests as well as a quasi-experimental pre- and postintervention interrupted time series regression analysis. Stool culture orders decreased by 24.4% (P < .001). There was a significant level difference and slope difference with linear regression. Five of the 11 hospitals had a significant reduction in stool culture orders. Stool O&P orders decreased by 18.2% (P < .01). Three of the 11 hospitals had a significant reduction in stool O&P orders. Our intervention successfully reduced inappropriate stool testing within a large safety-net hospital system.