Uncertainties in regional climate change simulations for the 21st century by five coupled atmosphere-ocean General Circulation Models (AOGCMs) (two of them including ensembles of simulations), for different anthropogenic forcing scenarios and 23 regions in the World, are examined. Seasonally and regionally averaged precipitation and surface air temperature for the future period of [2070--2099> as compared to the period of [1961--1990> are considered. The dominant source of uncertainty in the simulation of average regional climate change is due to inter-model variability with inter-scenario and internal model variability playing secondary roles. The range of predicted climate changes by different realizations of the same ensemble is small, and simulated changes exhibit a high level of coherency among different forcing scenarios. Uncertainties in regional changes are 3 K or greater for temperature and 25% of present day values or greater for precipitation. The model biases in reproducing present day climate are ≤1 K to over 5 K for temperature and ≤10% to over 100% for precipitation. ¿ 2000 American Geophysical Union