Analysis of this century's sea surface temperatures over the Pacific Ocean reveals an interdecadal oscillation with a period of 15--20 years. Our results show that the well-known 1976--77 climate regime shift is not unique, but represents one of several phase transitions associated with this interdecadal oscillation, also found around 1924--25, 1941--42, and 1957--58. The oscillation's striking north-south symmetry across the equator implies strong interactions between tropics and extratropics. A mode with a period of approximately 70 years and an apparently different spatial pattern is also identified tentatively but has to be evaluated further using longer time series. ¿ 2000 American Geophysical Union