Recent changes of water mass characteristics in the south Aegean Sea have considerably influenced the Eastern Mediterranean thermohaline circulation. A combination of salinity increase (1987-92) and temperature drop (1992-94) caused massive dense water formation and strong outflow towards the deep and bottom parts of the Eastern Mediterranean. This climatic shift, the most important since the existence of observations in the basin, is a combined effect of extreme meteorological events superimposed on large-scale trends. It has initiated a series of modifications in the hydrology and dynamics of the entire Eastern Mediterranean, with possible influence on the Mediterranean outflow in the North Atlantic Ocean. ¿ 1999 American Geophysical Union