A regular EGNOS Test Bed (ESTB) data collecting, 24 h per week, and analysis campaign has been developed by Eurocontrol along 2002 and 2003. During this period a geomagnetic storm was experienced on October 29th–31st 2003, degrading the ESTB performance in Europe. In this work we present a study of the effects of this storm in several European sites on October 30th. The ESTB performance is monitored from a network of GPS receivers widely distributed over Europe, including the ESTB reference stations (RIMS), and the geographical degradation of the accuracy is analyzed. Also, the correlation between the geomagnetic activity index with the number of events with protection level failures is shown. In the most severe stormy periods, the errors in the ESTB ionospheric corrections and its integrity bounds are analyzed to explain the peaks in the navigation system error, which produces Misleading Information events. This study is devoted to analyze the performance of the ESTB system, which is a simple prototype of the “true” final EGNOS system with several design limitations. [ABSTRACT FROM AUTHOR]