This study was done to provide basic data on prevention of breast cancer by identifying and analyzing risk factors for breast cancer in Korean women. The data were collected from three hospitals. The data from Jan. 1995 to Dec. 1997 was based on the patient recordings and personal contacts if possible. Data from 1998 to 1999 was collected from 280 inpatients and outpatients diagnosed as breast cancer. From this data, information about the risk factors of breast cancer could be acquired. The factors are scaled according to the degree of risk. Menstrual history, obstetrical history, family history. lactation period, life style were given 5 point, and body mass index was given 4 point. Using one-way ANOVA. the most important risk factors were identified and analyzed by multiple regression. The conclusion of this study are as follows : General factors which would show an effect on the results of the multiple regression included risk factors such as menstrual history, obstetrical history, lactation period, family history, and life style factors including mortal state, monthly income, educational level, job and age. Family history(R=0.481) was found to be the highest risk factor(23.1%) affecting breast cancer risk. The next factors were dying hair(R=0.603), drinking(R=0.846), body mass index(R=0.885), smoking(R=0.916), age of menopause(R=0.937), pregnancy age of first full-term(R=0.957), eating vegetable(R=0.980) and the number of full term pregnancies in that order. The sum total(R=0.986) of all the above factors accounted for 97.3% of the risk of breast cancer for Korean women. In conclusion, it was found that family history and dyeing hair were the highest risk factors for breast cancer. It is recommended that those with a family history of breast cancer should have regular breast examinations, and those who often dye their hair should reconsider this practice.