Ozonesonde measurements were performed annually in late winter and early spring from McMurdo Station, Antarctica, between 1998 and 2001, continuing a record starting in 1986. Mean column ozone during the same 47 day period in all four years are at least 11% below the average during the same period of the 1986--1997 record in the total column and at least 24% below the 1986--1997 record in the 12--20 km column. Average column ozone of 2000 and 2001 is also clearly below the minima observed between 1986 and 1997, with 2001 the lowest on record. These observations of lowest ozone are consistent with predictions and observations of peaking halogen abundance in the lower stratosphere around 2000 and a very slow decline thereafter. Such low ozone values are a combined consequence of stratospheric halogens and a continual and cold polar vortex. Man-released halogens mainly affect the 12--20 km ozone column, while the ozone column above and below the 12--20 km column stays about constant. Several kilometer deep ozone-depleted layers with mixing ratios below 0.1 ppmv appeared about 10 days earlier in 2001 than in 1998. Integrated ozonesonde measurements are compared to TOMS and Dobson spectrophotometer data with generally very good agreement. Measurement differences are largest when the vortex edge is close to McMurdo and decrease with increasing distance to the vortex edge region. The analysis of the vortex edge location at 400 K and 550 K shows that nearly all measurements were performed inside the polar vortex at 400 K, but extravortex air was sampled on occasion above 550 K. The earlier departure of the polar vortex edge above 550 K south of McMurdo led in 2000 to very high column ozone, both in the total column and in the 12--20 km column, which occasionally exceeds maximum observed values since 1986. Synchronous temperature measurements show correlations between high temperature, high ozone mixing ratio, and extravortex air.