The cathepsin D is a lysosomal protease secreted in excess by breast cancer cells. The function of this enzyme is degradation of the extracellular matrix and proteoglycan. It is induced by estrogens in estrogen receptor positive breast cancer cell lines. On the basis of this, cathepsin D expression in breast cancer cells seems to be correlated with the prognosis. But there is debates in its prognostic significance. Relationship between cathepsin D expression and other prognostic factors of breast cancer was studied. We investigated 51 cases of invasive ductal cell carcinoma of breast removed by open biopsy or mastectomy. All cases were fixed in formalin and embedded in paraffin. We used 46-KD intermediate form of the enzyme for cathepsin D expression on immunohistochemical stain. We observed no significant correlation with age, stage, histologic grade, lymphatic invasion, and estrogen receptor status. Cathepsin D may be an independent factor which is not related with other prognostic factors, especially estrogen receptor status.