The stable water isotopes HDO and H218O have been built into the latest version of the Hamburg atmospheric general circulation model ECHAM-4. First results of a 10 year control experiment (T42 resolution) are discussed in the paper, focusing on modelling the isotopic composition of precipitation over the Greenland ice sheet. The spatial distributions of δ18O and its two most closely related climatic parameters, surface temperature and precipitation, are in good agreement with observations over the inner ice sheet (mean δ18O at Summit: -34.6‰ observed, -35.1‰ modelled). Significant deviations between model results and measurements are observed only for coastal stations and around Dye3 (-27.8‰ observed, -23.9‰ modelled). These deviations can partly be explained by the coarse model resolution. The spatial linear relationship between surface temperature and mean 18O concentration (the 'Dansgaard slope') is well reproduced by the model. A detailed comparison of the seasonal cycle of the isotopic composition in precipitation and ice core measurements shows good agreement not only for the seasonal phase of δ18O and δD but also for the deuterium excess d. The absolute amplitudes of the modelled isotope signal are overestimated, however. Peak to peak variations in the seasonal cycle of the isotopes are higher in the model than in ice core analyses (seasonal δ18O variations at Summit: 8-10‰ observed, 20-25‰ modelled). Post- depositional processes in the snow might explain this deviation between the model results and observations.