Extreme storms registered by the urban rain gauge network installed and supported by CLABSA (Clavegueram de Barcelona S. A.) in Barcelona in the period 1994–2001 have been investigated. Eleven rain events presenting intensities for durations between 5 min and 24 h with return periods equal to or larger than 5 years for any of the network gauges have been found. A cluster analysis has yielded four main classes of extreme rainfall events in this area, related to the meteorological scales involved: local (18%), mesoscale (37%) and synoptic storms (27%), as well as more complex rain events originated by multiscale mechanisms acting together (18%). An intensity index to classify extreme rainfall events in order to their complexity and severity, taking into account the contribution of the different scales implied in the rainfall processes, has been calculated. The frequency distribution of the intensity index values obtained for the urban network has resulted very similar to that calculated for rain data recorded by the Jard´ı gauge of the Observatory Fabra of Barcelona during 1927–1992 inclusive.