A stable cohort (n = 369,725) was reconstructed to test the association of hepatitis B virus (HBV) infection with subsequent occurrence of liver cancer in a healthy Korean population. The cohort consisted of male beneficiaries of the Korea Medical Insurance Corporation over 30 years of age, living nationwide. The HBV infection was tested by the reversed passive hemagglutination method for the HBsAg and by the passive hemagglutination method for the anti-HBs at the time of recruitment in 1984. Admissions due to liver diseases were identified through a computerized system for reimbursements on medical insurance claims from January 1, 1985 to December 31, 1987. For a more valid estimate of incidence, a sample survey was carried out, obtaining correction coefficients against misclassification of the diagnosis, as well as those for duplicate claims in a year. The incidence rate of liver cancer steadily increased with age (kappa 2 TREND = 51.1, df = 1, p = 0.00).(ABSTRACT TRUNCATED AT 250 WORDS)