The control run of the Hadley Centre-coupled climate model (HadCM3) is used to establish the sources of multidecadal/centennial sea level (SL) variations in the northwest Atlantic. It is shown that variations in the sea level for the largest part of this area are related to variations in the thermohaline structure of the upper (≈500 m) part of the ocean. Temperature variations dominate steric sea level variations, while salinity variations are dominant only in the margins of the Labrador Sea and near the Mediterranean outflow. In the Labrador Sea, lower layers in the ocean also contribute to the variability in expansion/contraction of the water column. It is shown that along the North American East Coast, variations in the thermohaline structure of the water column are predominantly related to variations in the wind-driven circulation rather than the thermohaline circulation, which dominates the thermohaline structure in the central parts of the North Atlantic. In the Gulf Stream area and near the Labrador Current, sea level has on the multidecadal/centennial time scale a strong barotropic signal superposed on steric sea level variations.