This paper estimates global changes in ultraviolet radiation since preindustrial times, resulting from anthropogenic stratospheric and tropospheric ozone changes. A sophisticated radiative transfer scheme is employed to calculate changes in the diurnally integrated UVB (defined here as 280–320 nm) and erythemally weighted (EER) irradiance reaching the Earth's surface. Stratospheric ozone changes are obtained from combining total ozone mapping spectrometer satellite data with Dobson ground-based instrument data. Tropospheric ozone changes are estimated from the University of Oslo three-dimensional chemical transport model. These ozone trend data are combined in three ways to calculate the associated ultraviolet trend and estimate its uncertainty. We show that in low latitudes a significant (up to 5% for UVB and 9% for EER) decrease in surface UV may have occurred, due to tropospheric ozone increases. Large UV increases are found at high latitudes, with up to 60% increases in October and 20% increases in April. The possible effects of soot and sulphate aerosol changes on the UV are also briefly examined; increased aerosol amounts may have decreased surface UVB and EER by up to 7% locally and about 2% on a global average.