The basic parameters of extra-tropical cyclones in the northern Baltic are examined in relation to extreme sea level events at Estonian coastal stations between 1948 and 2010. The hypothesis that extreme sea level events might be caused not by one intense extra-tropical cyclone, as suggested by earlier researchers, but by the temporal clustering of cyclones in a certain trajectory corridor, is tested. More detailed analysis of atmospheric conditions at the time of the two most extreme cases support this concept: the sequence of 5 cyclones building up the extreme sea level within about 10 days was very similar in structure and periodicity.