Schiphol Airport is the only airport in the Netherlands where trans-Atlantic flights arrive. Its Municipal Health Services (MHS, GGD Kennemerland) and the Center for Infectious disease Control (CIb-RIVM) frequently experienced that, despite all efforts, the time period elapsing from exposure to administration of the first oseltamivir dose exceeded the required 48 h. Acquiring contact details from airlines was time consuming, and contact details on passenger lists were often minimal, so that contacts were difficult to trace. In this study, we assess the time delay in contact tracing of flight passengers for influenza A/H1N1 2009 as performed in the Netherlands during the initial phase of the pandemic. Our data show that despite all efforts the effectiveness of this control measure in daily practice is minimal.