Information regarding the status of common eiders Somateria mollissima breeding in the Canadian Arctic is lacking. In 1997, we surveyed five island archipelagoes in the Belcher Islands in Hudson Bay (56 00'-57 30'N, 79 30'-80 00'W) from 3 - 23 July 1997. Our results were compared with eider surveys of the same islands completed between 1985-89 using a standard protocol. This study represents the first population trend data of any common eider population breeding in the eastern Canadian Arctic. 1416 nests were found on 431 islands; most (94.1%) while the female was still incubating. In every region, the number of nesting eiders declined significantly (overall = 75.0%, range: 62.3% - 84.0%). In 1997, nesting islands and adjacent waters were free of ice, eiders laid large clutches (range: 4.0 - 4.4, 1.0-1.2 SD), and, they nested early. These conditions are indicative of a good nesting season, and we conclude that extensive non-breeding by female eiders in 1997 does not account for the observed decline. A large die-off of eiders during the winter of 1991-1992, which occurred when areas of open water froze, is the most likely cause of the decline. Our results present serious conservation concerns because eider populations are sensitive to reductions in adult survival, and this population is harvested throughout the year by subsistence hunters.