Surface truth data, including an empirical tide model, geoidal undulations, dynamic heights, and infrared imagery in the Geos 3 Atlantic calibration area, have been compared with features in Geos 3 altimeter profiles of sea surface height. The 5'¿5' gravimetric geoid computed by J. G. Marsh agrees with altimeter profiles to the level of the sea surface topography (~50 cm). After removal of a low-degree polynomial the differences of collinear passes of altimeter data reveal apparent time-dependent ocean surface features. Some of these can be identified from the surface truth information, but others cannot be correlated with known features, probably owing to limitations of the surface truth data. Independent collinear pairs also indicate that the best of the many orbit computation models used to compute the Geos 3 altitude ephemeris introduces a bias of about 1 m (rms) on a typical pass of altimeter data.