Measurements of OClO total column amounts by means of the Global Ozone Monitoring Experiment (GOME) instrument conducted in the austral and boreal winter stratospheres from 1995 through 1999 are presented. GOME is a four-channel UV/visible spectrometer (240--790 nm) deployed on the polar orbiting European ERS-2 satellite since April 1995. Previous studies have shown that the observations of OClO, the symmetric chlorine dioxide formed in a side channel of the reaction of BrO+ClO, can serve as an indicator for a stratospheric chlorine activation. GOME's 3-day coverage of the global atmosphere allows us to infer the first global data set of OClO, and to study continuous time series of its occurrence in both winter stratospheres. It is found that, while OClO regularly occurs over Antarctica in similar amounts and seasonal timing during the different winters, its occurrence is much more variable in the Arctic winter stratosphere, primarily because of the larger dynamic activity that result in warmer temperatures there. About 40% higher OClO column amounts are found in the Antarctic polar stratosphere than in its northern counterpart, a further indication for a significantly more efficient chlorine activation in the Antarctic than the Arctic late winter and spring stratosphere. ¿ 2001 American Geophysical Union