**Objective:** Hospital visitors pose a risk for transmitting pathogens that can cause health care–associated infections. The present study aimed to test an evidence-based intervention to improve visitors’ hand hygiene behavior through persuasive messages. **Method:** For the 14-week-long field experiment, 7 signs were designed according to the principles of persuasion proposed by Cialdini: reciprocity, consistency, social-proof, unity, liking, authority, and scarcity. Each sign was displayed on a screen for 1 week directly above the hand-rub dispenser in a hospital lobby. After each 1-week posting, the screen was blank for 1 week. **Results:** An electronic monitoring system counted 246,098 people entering and leaving the hospital’s lobby and 17,308 dispenser usages. The signs based on the authority and the social-proof principles significantly increased the hand-rub dispenser usage rate in comparison to the average baseline usage rate. **Conclusions:** These results indicate that simple and cost-efficient interventions can initiate expedient behavior change in hospitals. However, the findings also highlight the importance of careful planning and rigorous pretesting of material for an intervention to be effective. Theoretical and practical implications of these findings are discussed.