The vertical distribution of ozone at Marambio (64¿S, 56¿W) has been studied using ozonesonde measurements for 1990--1999. Total ozone has been studied using Dobson spectrophotometer measurements for 1987--1999. Marambio is well placed to study the Antarctic ozone depletion mechanism because it is frequently located inside, outside, and in the edge region of the polar vortex and sees the early return of sunshine in late winter. The ozone data have been classified according to the location of the polar vortex with respect to Marambio. The vortex edge definition based on potential vorticity (PV) and its gradient has been compared to two other methods. The method used here gives better results than the use of predetermined PV limits or the use of maximum PV gradient only. The Marambio total ozone records have been compared to the 11-year (1957--1967) record of the nearby Argentine Islands (65¿S, 64¿W) to estimate long-term ozone changes over the Antarctic Peninsula. The largest decreases of ozone during 1987--1999 were observed in the lower stratosphere in July--August in the polar vortex edge region, as well as inside the vortex in September--October. Our analysis does not give indications of an ozone recovery so far. The Marambio data show that since the mid-1990s the magnitude of the seasonal ozone decline inside and in the edge region of the vortex has remained at roughly a constant level. Outside the vortex in September--December, as well as from midsummer to midwinter (January--June), ozone levels have remained practically unchanged during the whole period from 1987 until 1999.