Until recently, very little was known about the basic ecology of the Harlequin Duck (Histrionicus histrionicus) in eastern North America, including molting locations. A combination of aerial, ground and boat surveys were initiated in 1989 (Québec) and 1994 (Newfoundland and Labrador), and continued through 1999, to locate their molting areas. Molting Harlequin Ducks were found in Labrador, Newfoundland and the Gaspé Peninsula and Anticosti Island, Québec. Coastal areas of southern Labrador, Grey Islands, northern Newfoundland, and Bonaventure and Anticosti Islands, southern Québec, were the most important sites. The tip of northern Labrador and possibly sites along the Québec North Shore and Greenland are the most likely sites where the rest of the eastern population molts. Molting chronology for the ducks in Québec is similar to those on the east and west coast of North America. Now that these sites are known, monitoring and, if necessary, protection of these sites can be considered.