The authors conducted a nationwide survey to estimate the incidence rates of female breast cancer among Korean women in 1990-1991. We identified potential breast cancer cases based on the claims sent by medical care institutions throughout Korea to the Korea Medical Insurance Corporation (KMIC) from January 1988 to December 1989, whose diagnoses in the claims included one of the following diagnostic codes; ICD-9 174-175 (malignant neoplasms of the breast), 217 (benign neoplasms of the breast), 610-611 (benign mammary dysplasia and other disorders of the breast), 233 (carcinoma in situ of the breast and genito-urinary system), or 195-199 (malignant neoplasms with uncoded sites). In order to collect the final diagnosis of the potential cases, abstracting medical records was performed through visiting or mailing an abstracting format to the corresponding medical institutions. Thereafter oncologists reviewed the abstracting formats and confirmed the incident cases of female breast cancer among the potential breast cancer cases. Using these data from the KMIC, the incidence patterns of female breast cancer among Korean women were estimated as of July 1, 1988 to June 30, 1989. The incidence rate of female breast cancer adjusted for the Korean population was estimated to be 9.9 (95% confidence interval: 9.5-10.4). The cumulative rates for the ages 0-64 and 0-74 were 0.85% and 1.0%, respectively. The standardized rate for the world population was 10.9, which was lower than those of any other Asian country including China and Japan in 1983-1987.(ABSTRACT TRUNCATED AT 250 WORDS)