The number of Harlequin Ducks (Histrionicus histrionicus) wintering in eastern North American is small, and little was known about these birds, especially their breeding distribution. During the breeding period, 990 km of river and streams on Newfoundland's North Peninsula was surveyed where 69 Harlequin Ducks were sighted. Breeding densities varied among watersheds (range 0-0.090 males/km), were slightly lower than elsewhere in eastern North America, and lower than in western North America and Iceland. A total of 128 ± 45 males (indicated pairs) or 284 ± 89 birds (±95% CI) was estimated to occur on the North Peninsula during the breeding season. This may represent 20% of Harlequin Ducks wintering in eastern North America and highlights the importance of the Northern Peninsula as a breeding area for this rare duck.