BACKGROUND: The frequency of invasive lobular carcinomas is about 3% to 15% of all breast carcinomas. It is known that an invasive lobular carcinoma is different from other forms of breast cancer in the aspect of clinical characteristics and metastatic pattern. METHOD: To search of clinical characteristics of invasive lobular carcinomas, we restrospectively investigated 31 cases of invasive lobular carcinomas that had been treated from 1985 to 1996 at the Department of Surgery, Severance Hospital. RESULTS: The peak incidence was in the 40's (12 cases, 38.7%), and the average age was 45.8. The main clinical manifestation was a palpable mass on the breast at the time of visit to the hospital (30 cases, 96.8%), and the most frequent site was the upper outer quadrant (18 cases, 58.1%), followed by the upper inner quadrant (6 cases, 19.4%), of the breast. The most prevalent tumor size was 2-4 cm (14 cases, 45.2%), and the mean size was 3.27 cm. The negativity of the axillary nodes for invasive lobular carcinoma was 67.7%. According to the TNM system, there was 5 casess (16.1%) in stage I, 17 cases (54.8%) in stage IIa, 7 cases (22.6%) in stage IIb, and 2 cases (6.5%) in stage IIIb. The positivity of the estrogen receptor (ER) was 35.7%, and the positivity of the progesterone receptor (PR) was 54.5%. The overall 5-year survival rate was 82%, the overall 5-year disease-free survival was 70%, and the mean survival was 108 months. CONCLUSION: The clinical characteristics of an invasive lobular carcinoma seem to be similar to those of an invasive ductal carcinoma. Further studies are required to search for the clinical characteristics and for an adequate treatment.