Data were analyzed from 1110 thyroid cancer cases between 1960 and 1984 identified by the Hawaii Tumor Registry, a population-based Statistics, Epidemiology and End Results (SEER) participant covering the entire state of Hawaii. Incidence rates for men and women were relatively stable during this 25-year period. The overall age-adjusted rates were 8.1 per 100,000 for women and 3.1 per 100,000 for men. There was a significant variation in incidence on the basis of ethnicity, with the highest rates for women occurring in Filipinos (18.2 per 100,000) and for men in Chinese (6.3 per 100,000). A comparison of different populations around the world showed that Hawaii has some of the highest reported incidence rates for thyroid cancer. In addition, a comparison of ethnic-specific incidence rates for groups living in Hawaii with people of the same ethnic backgrounds living in other geographic areas showed that Hawaii residents generally have much higher rates, suggesting that environmental influences are responsible for the unusually high rates in Hawaii.