We conducted seabird surveys along the entire coast of the Chukotka Peninsula (northwestern Siberia, Russia) from 1983 to 1991. We present the first comprehensive descriptions of the distribution and size of Chukotkan seabird colonies. Thirteen species of seabirds were recorded breeding on the peninsula, with an additional 13 migrant or vagrant species. Our estimate that at least 3 300 000 seabirds breed on the Chukotka Peninsula demonstrates the importance of this region to arctic seabird populations. Colony size and species composition may be determined by availability of adequate breeding sites, access to foraging areas, and variable ice conditions.