Studies of the amount of total ozone at many observatories show that the negative 1983 deviation from the long-term average exceeded 2σ, and was the greatest in magnitude for an annual deviation in their entire record., the total ozone in December 1982 and first few months of 1983 decreased by more than 10% below its normal amount. Only during late 1983 did the total ozone recover to near normal values. It remained close to normal during most of 1984 but decreased sharply again in February–April in the Northern Hemisphere, and in June–September 1985 in the Southern Hemisphere. Only toward the end of 1985 and in 1986 did the total ozone recover to its long-term average amount. These ozone changes are confirmed by satellite observations to be truly global events, although with some time lag between different latitudes. The 1983 and 1995 changes in total ozone are also examined by analyzing the deviations of ozone partial pressure at different altitudes. This analysis reveals the times and the layers of the changes, as well as their net contributions to the total ozone deviations. It is concluded that periods of total ozone deficiency were mainly due to changes in ozone amount in the lower and middle stratosphere, which suggests that circulation effects were dominant. The appearance of different partial contributions by the lower vs middle stratospheric layer is noted. Looking at the past 20-yr record in perspective, an important finding emerges that the observed ozone deficiencies are consequences of the quasi-biennial oscillation (QBO) in combination with the very pronounced circulation changes during the 1982/83 El Nino–Southern Oscillation (ENSO) event. The physical and photochemical processes triggered by the April 1982 El Chichóeruption, leading to partial ozone depletion, are also recognized and critically asessed. However, the results of the analysis suggest that the QBO, as has happened many times before, has “set the stage” for major ozone deficiencies both in 1983 and in 1985, and the ENSO and El Chichóevents only served to augment the effect in the 1982/83 episode.