Introduction: The Hawthorne effect, or behaviour change due to awareness of being observed, is believed to inflate directly observed hand hygiene compliance rates, but evidence is limited. Methods: A real-time location system tracked hospital hand hygiene auditors and recorded alcohol-based hand rub and soap dispenses. Rates of hand hygiene events per dispenser per hour within sight of auditors were compared to dispensers not exposed to auditors. Results: The event rate in dispensers visible to auditors (3.75/dispenser/hour) was significantly higher than unexposed dispensers at the same time (1.48) and in prior weeks (1.07). The rate increased significantly when auditors were present compared to five minutes prior to arrival. There were no significant changes inside patient rooms. Conclusions: Hand hygiene event rates increase in hallways when auditors are visible and the increase occurs after the auditors' arrival, consistent with the existence of a Hawthorne effect localized to areas where auditors are visible.