This article describes a retrospective and descriptive study into the added value of ProMED-mail--the global electronic reporting system for outbreaks of emerging infectious diseases and toxins maintained by the International Society for Infectious Diseases--as an early warning system for The Netherlands Early Warning Committee (NEWC). Information about infectious disease events in foreign countries originating from ProMED-mail was retrieved from the reports of the NEWC between May 2006 and June 2007. Each event was analysed in depth in order to determine if it could have been a possible threat to public health in The Netherlands. It was determined whether these events were mentioned in other sources of information used by the NEWC besides ProMED-mail. In addition, we assessed the possible consequences of missing an event when not reading ProMED-mail or of being informed of the event with a time delay. Semi-structured interviews with stakeholders were conducted to explore other functions of ProMED-mail besides early warning. Five out of 25 events reported in ProMED-mail were assessed as a potential threat to The Netherlands, mainly because of the known vulnerability of The Netherlands for vaccine preventable diseases: an outbreak of measles in the United Kingdom and Japan, a case of poliomyelitis in Kenya, and two events concerning Highly Pathogenic Avian Influenza (HPAI) H5N1. The outbreak of measles in Japan and one case of HPAI H5N1 infection in a bird in Germany were only reported by ProMED-mail; the other potential threats were mentioned in other sources with a time delay. ProMED-mail has a limited but real added value over other sources in the early warning of threats. A more specific approach of using ProMED-mail by defining vulnerabilities of a country would be useful and efficient. ProMED-mail is appreciated for providing background and preliminary outbreak information.