We compared incidence rates of primary cancer of the thyroid among United States-born and foreign-born Chinese, Japanese, and Filipino residents of the US with rates among US-born Whites. Thyroid cancers diagnosed between 1973 and 1986 occurring among individuals 15 to 84 years of age residing in western Washington state, the San Francisco-Oakland (California) area, or the state of Hawaii were included in the analysis. Population estimates by age, gender, ethnicity, and country of birth were obtained for these areas from the US Bureau of the Census. Filipino women born in the Philippines had 3.2 (95 percent confidence interval = 2.7-3.8) times the rate of thyroid cancer of US-born White women, while US-born Filipino women were not at any increased risk. Philippine-born Filipino men also had a relatively high rate of thyroid cancer (relative risk [RR] = 2.6), more so than US-born Filipino men (RR = 1.5). Among Japanese, risk of thyroid cancer varied by birthplace, but the direction of the association differed by gender and by histologic type of cancer. No clear association with birthplace was noted among Chinese men or women. These data suggest that persons residing in one or more regions from which Filipino-Americans migrated have been exposed to environmental influences that have increased their subsequent risk of thyroid cancer.