In this study, the value of CA 15-3 as a tumor marker was measured in 87 patients with breast cancer and 3 patients with benign breast cyst. 32 healty women were selected as a control gruop. The value of CA 15-3 was compared between the control group (n = 32), the group of NED breast carcinoma patients and the group of patients with distant metastasis from breast carcinoma (n = 87). The result of this study shows that the value of CA 15-3 between the control group (n = 32) and the breast carcinoma group (n = 87) was statistically significant (p 0,001). In addition to that the same significant level was also noticed in the group of NED breast carcinoma and the group of patients with distant metastasis from breast carcinoma. However-there was no significant value found between control group and the group of NED plus local recurrent patients. We think CA 15-3 measurement may be valuable as a tumor marker in detection of metastatic breast disease.