PURPOSE: Obesity has been shown to have important effects related to breast cancer. But there have been few data available on the distribution of body mass index (BMI) among Korean breast cancer patients and on the effects of this distribution on patient prognosis. Therefore we investigated the BMI distribution of Korean breast cancer patient's and its relationship with other tumor markers, in order to elucidate the relationship between BMI and patient prognosis. METHODS: We measured the BMI of 266 Korean adult women with breast carcinoma.and divided the subjects into the following subgroups according to BMI; low body weight (BMI<20), normal body weight (BMI; 20~25) and over weight (BMI>or=25). We compared this distribution with that of the general Korean women's population. and investigated the correlation with other prognostic factors and tumor markers. The 5 year overall and disease free survival rates were evaluated for both the total breast cancer patients and the adjuvant hormone treated breast cancer patients, according to BMI subgroup, using the Kaplan-Meier method. RESULTS: Mean BMI for the breast patients was 23.4+/-3.1, and did not differ from that of the general Korean adult women's population ('1994 National Nutrition Survey Report). BMI increased with increasing age and was highest in the 60~69 yr age group. BMI was correlated with tumor size and stage. The survival rates were low in the high BMI group among both total and adjuvant hormone treated breast cancer patients, but in neither was any statistical difference found between BMI subgroups. CONCLUSION: Korean breast cancer patients are not obese as the general population and their BMI increases with increasing age and menopausal status. There was a tendency for higher BMI to be associated with poorer prognosis, although not to a statistically significant degree.