The Seasat radar altimeter was designed to operate over the open ocean and encountered problems over sea ice. In particular, the on-board measurements of surface height were noisy and unreliable. As a consequence, published mean sea-surface and geoid maps based on the Seasat on-board height estimates either omit sea-ice-covered areas or include suspect data. We have identified and investigated the problems encountered by the Seasat altimeter over sea ice and have developed a technique for extracting accurate surface-height values from the sea-ice echo wave-form data. The retracking method is based upon fitting real wave forms to a library of model returns.