Breast cancer is one of the most feared health problems in women ; Recent studies revealed that it had come up to be the second most in this country and high prevalent disease in the western countries among breast disease in women. However, early detection of the cancer mass is known to be easier than in many other malignancies. This study was performed to investigate the various characteristics of patients of brea st cancer; by the structural variables, menstrual, marital, and child bearing, and also their understandigs and attitude towards the disease. A hundred and in- and out- patients of St. Mary's Hospital and National Atomic Institute, Seoul were sampled. Data were gathered through direct interview by the researcher from February 1976 to January 1977 and the clinical records were used as references . Results are as follows ; 1. Breast cancer revealed to be most prevalent in the forties; average age of 45.2 years. 2. The average age of menarche revealed to be 15.4 years ; the largest group were the 16-20 years (N = 75, 68.2%). In 55 cases (50%.) menstruation were normal, 38 (34. 5%) postmenopause and only in 17(15.5%), menstruation revealed irregularity. 3. The average marital age revealed to be 22.3 years; the largest group were 21-25 group (N=43, 39.1%). The average duration of marital life revealed to be 24.7 years; 11-20 years group were the largest (M= 34, 30.9%). 4. Most of the patients revealed to have pregnancy experiences (N= 100, 90.9%) ; the average rate of experience were 5.3 times the largest group were 3.4 times group(N=32, 29.1%). 54 patients (49. 1%) revealed to have had abortion experience; the average were 3.4 times. 5. The largest group (N= 77, 70%) had been breast feeding, followed by mixed feeding (N = 12, 10.9%) and artificial feeding(N = 10, 9.1%). 6. Personal health history revealed that in 20 patients (18.2%) revealed to have the past history of purulent mastitis, 5 ps.tients (4. 5%) of breast cancer and 3 patients (2. 7%) of uterine cancer family history. 7. In the one half(N = 56, 50.9%), they had had some information about breast cancer ;27 (24.5%) by mass media, 12(10.9%) through personal contacts and 17(15.5%) were not able to classify the source of information. 8. In 55 cases (50%) the cancer mass were discovered incidentally, in 39 cases (35.5%) by manual detection by self, in 10 eases (9%) by others and in 6 cases (5. 5%) by observing subjective symptoms. 9. The average duration lapsed between the discovery of cancer mass and the visit to the hospital revealed to be 9.4 month. Chief reason for the delay revealed to be the non-chalancy due to the absence of pain(N = 50, 45.5%) followed by the administration of herb and commercial medication (N = 19, 17.3%). 10. The left side breast was more affected than the right side breast, represent by 60 cases in the left and 39 cases in the right. The most frequent site of the breast cancer was the upper-outer quadrant in 53 cases(47.'/%), and followed by the center in 20 cases(18 %), and the uppe inner quadrant, in 19 cases(17.1 %). There was / cases of bilateral carcinoma. The most prominent symptom was painless mass.