A systematic intercomparison of three realistic eddy-permitting models of the North Atlanticcirculation has been performed. The models use different concepts for the discretization of thevertical coordinate, namely geopotential levels, isopycnal layers, terrain-following (sigma)coordinates, respectively. Although these models were integrated under nearly identicalconditions, the resulting large-scale model circulations show substantial differences. The resultsdemonstrate that the large-scale thermohaline circulation is very sensitive to the modelrepresentation of certain localised processes, in particular to the amount and water massproperties of the overflow across the Greenland-Scotland region, to the amount of mixing withina few hundred kilometers south of the sills, and to several other processes at small or sub-gridscales. The different behaviour of the three models can to a large extent be explained as aconsequence of the different model representation of these processes.