Size: L: 25 cm. Wt: Males: 50 g. Females: 70 g. This species is sexually dimorphic in size, and also in color during the breeding season, with females being more intensely-colored. Wilson's Phalarope is also seasonally dimorphic.

Breeding Male: back and wings mottled dark brown and blackish; head white, with broad black stripes over crown and through eye, meeting and curving down sides of neck, becoming dark reddish-brown on neck; throat white; breast with reddish wash; belly and undertail coverts white; bill long, very narrow, with blackish upper mandible and yellowish lower mandible; legs blackish

Breeding Female: back blackish, with distinct grey chevron; wings dark slate, with rufous wash over scapulars; head whitish, with dark grey crown stripe, and broad, black stripe running through eye and curving down neck, becoming dark rufous on neck; throat white; breast with rufous wash; belly and undertail coverts white; bill and legs as in breeding male

Winter Adult: back and wings dark grey; head whitish, with broad grey crown stripe and thin grey eye-stripe; throat, breast, belly, and undertail coverts white; bill dark; legs blackish