We monitor and model the effects on world-wide temperatures of the June 1991 volcanic eruption of Mount Pinatubo in the Philippines. Global mean air temperatures were reduced, by up to 0·5°C at the surface and 0·6°C in the troposphere, for some months in mid-1992, in approximate accord with model predictions. Differences from these predictions occurred in the Northern Hemisphere winters of 1991–1992 and 1992–1993, as a result of atmospheric circulation changes that yielded continental surface warmings not fully reproduced by the model. The effects of the eruption were less evident by 1994. A superposed-epoch composite for five major tropical eruptions shows significant global post-eruption cooling at the surface when the effects of the El Ni7o–Southern Oscillation are removed from the data. Stratospheric warmth following Pinatubo lasted until early 1993 according to Microwave Sounding Unit data.