Satellite data have revealed the presence of an intens4e mesoscale anticyclonic eddy at the northern boundary of the Balearic Sea, which appeared in September 1998 and remained almost stationary until March 1999. Sea Surface Temperature (SST) images have allowed to investigate the formation of the eddy indicating an entrance of Atlantic Water through the Ibiza and Mallorca channels much stronger than normal conditions and following an anomalous path. Additional data form an oceanographic cruise on February 1999 confirmed the signature of Atlantic Water in the region. This structure produced a relevant inversion in the usual cyclonic circulation of the basis. The observed strong anticyclonic eddy induced anomalous northeastwards geostrophic velocities near the Catalan Coast reaching the maximums of about 50 cm/s, by contrast of the typical 20 cm/s in opposite sense. The three data-sets examined in this work are in good agreement in terms of the dimensions and intensity of the eddy. This suggests that remote sensing would be able to detect such kind of events in the future constituting a powerful tool providing a real-time monitoring of the Basin.