To study the effect of pre-operative biopsy for breast cancer on the 10-year-survival rate, 1123 cases with single cancer radically operated at the Cancer Institute Hospital between Jan. 1960 and Dec. 1969 were analyzed. The survival rate in 292 biopsied and non-biopsied patients with cancers less than 2 cm in diameter and no lymph node metastasis was not significantly different. There was no difference between incisional- and excisional-biopsied patients. However, the survival rates tended to decrease as the interval between biopsy and radical surgery increased. We conclude that pre-operative biopsy does not worsen the prognosis in patients with breast cancer. Early detection and treatment are of great importance.