Total ozone data available from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) have been compared with Version 7 of the Nimbus 7 (for the 1978--1993 period) and Meteor 3 total ozone mapping spectrometer (TOMS) data sets (for the 1991--1994 period) and with Version 6 of the Nimbus 7 solar backscattered ultraviolet (SBUV) data set (for the 1978--1990 period). Comparison between the ground-based and satellite observations resulted in parameters such as bias, scattering, relative trend, and seasonal component. About 80% of all Dobson, Brewer, and filter ozonometer stations have standard deviations of monthly mean differences with TOMS that are less than 2.5%. Typically, results of the comparisons between ground-based stations and SBUV are similar to those for ground-based and TOMS comparisons. For the ground-based direct sun total ozone measurements the standard deviations between TOMS and Dobson daily mean values are about 2.4%. The standard deviations for Brewer and filter ozonometer stations are 2.2 and 3.5%, respectively. For the less accurate zenith sky measurements, standard deviations are 3.8% for Dobsons, 4% for Brewers, and 4.7% for filter ozonometer data. Comparisons of individual ground-based measurements with satellite overpasses yield standard deviations which for middle latitudes increase approximately linearly from about 2% at coincidence to 6% for a 24 hour difference in time or a 600 km spatial difference. Typical problems with ground-based observations and results of the comparisons for individual stations are also discussed. ¿ 1999 American Geophysical Union