The late Quaternary plinian eruption forming the Kos Plateau Tuff on the island of Kos, Greece, was one of the largest in the Mediterranean. A precise date for this eruption would significantly improve the chronology of the deep-sea tephra layer W-3, because reliable correlation of W-3 with the Kos Plateau Tuff has been previously established. We have dated sanidine from the eruption at 161.3¿1.1 ka using the laser-fusion single crystal 40Ar-39Ar technique. This age represents a significant refinement over both conventional and highly precise (Cassignol method) K-Ar ages, and the 40Ar-39Ar age is shown to be in remarkably good agreement with the age of W-3 inferred from recent astronomically calibrated oxygen isotope chronologies. ¿ American Geophysical Union 1996