The medical records of inpatients with diagnoses of either ICD-9 193(malignant neoplasm of the thyroid gland) or 226(benign neoplasm of the thyroid gland) in the claims sent in by medical care institutions throughout the country, to the Korea Medical Insurance Corporation (KMIC) during the period from January 1, 1986 to December 31, 1987 were abstracted. These records were abstracted in order to identify and confirm new cases of thyroid cancer among the beneficiaries of the KMIC. Using these data, the incidence rate of thyroid cancer among Koreans was estimated as of July 1, 1986 through June 30, 1987. The crude rates were estimated to be 0.76(95% Cl: 0.63-0.87) and 3.87(95% Cl: 3.60-4.14) per 100,000 in males and females, respectively, and the cumulative rates for the age spans 0-64 and 0-74 in males were 0.06% and 1.10%, respectively. In females, those were equally 0.35%. The age-adjusted rate for the world population was 0.93 per 100,000 in males, which is one of the lowest levels in the world. However, the adjusted rate in females was 3.96 per 100,000, which is an average level and very similar to that of the Chinese in Singapore and Shanghai. A similar tendency was shown in the case of the truncated rates for the age group of 35-64, which was 1.91 per 100,000 in males and 8.82 per 100,000 in females.