The impact of Greenland's orography on the general circulation is investigated. Two 10 years simulations were conducted using the NCAR Community Climate Model (CCM3), run at T106 horizontal resolution, a control simulation and a simulation were Greenland's orography was set to sea level. A comparison of the simulations indicates that Greenland has a significant impact on the general circulation at middle and high latitudes on the Northern Hemisphere. The storm tracks over the North Atlantic have a larger northerly component in the presence of the mountain. The difference fields of sea level pressure, geopotential height and temperature have a wavelike pattern that extends around the earth. The first wave of this pattern is linked to the blocking and diversion of cold low level air masses west of Greenland. The result is a trough on the upstream side of the mountain. Thus, Greenland's impact on the general circulation is fundamentally different from the impact of the Rocky Mountains and the Tibetan Plateau where a trough is created downstream of the mountains.