This report presents findings of a 1990 field survey for harlequin ducks (Histrionicus histrionicus) in northwest and west-central Montana. A brief overview of the natural history and habitat requirements of harlequin ducks is included. A total of 45 streams, 37 on the Kootenai National Forest (KNF) and 8 on the Lolo National Forest (LNF), were surveyed between May 5, 1990 and August 31, 1990. Harlequin ducks were observed on 39 occasions. A minimum of 27 individuals were identified. Of the 27 individuals, 6 were males, 7 females and 14 juveniles. The harlequins were located on 7 streams on the KNF: Big Creek, Callahan Creek, Grave Creek, Kootenai River, Marten Creek, Swamp Creek and the Vermilion River. Harlequins were located on 1 creek on the LNF: Trout Creek. Broods were located on Big Creek, Callahan Creek, Marten Creek and two on the Vermilion River, for a total of 5 broods. The sightings on Callahan Creek and Big Creeks are the first confirmed sightings of breeding harlequins on those streams. Brood size of the 5 broods ranged from1 to 3 individuals with a mean of 2.3. Hatching was estimated to occur mid-late June. Harlequins were found on streams ranging 5 m to over 30 m wide. Stream flows ranged from 24 cfs to >4000 cfs. Stream gradients were between 1.8 % and 2.8%. Harlequins were found in assortment of habitats. Common to all the occupied streams was the presence of beaver activity, str4eam braiding or multiple channels, moderate to dense stream side vegetation, and a flyway above the stream mostly clear of overhanging vegetation. A decrease in duck number and brood size was observed compared to 1989. It is unclear if the decrease reflects a downward population trend, a normal fluctuation in the population, or is a function of survey methods.