Analysis of the first 5 years of TOPEX/Poseidon altimetry data reveals that mesoscale variability (MV) in the Kuroshio Extension region has a large, well structured temporal change. The mesoscale variance varies by more than a factor of 2 over the 5-year span. The temporal variation appears to be the combination of two forms: a large-scale standing (from 140 ¿E to 170 ¿E) modulation, and accompanying with it a variation that propagates westward slowly with a phase speed of about 0.7 cm/s. Along with the westward propagation, the center of maximum MV retreats westward. As a comparison, variation of MV in the Gulf Stream region is computed. The analysis shows that MV in the Gulf Stream region also undergoes large temporal change. But it is much less well structured. ¿ 1999 American Geophysical Union