Because carcinoma of breast is known to readily metastasize to the bone, early detection of metastasis spread is very important. Two hundred thirty four consecutive patients who had $^{99m}Tc-MDP$ bone scans prior to treatment and during the follow up period were studied retrospectively to determine the contribution of the scans to staging, treatment and follow up examination between Jan. 1980 and Apr. 1987 in Seoul National University Hospital. 1) Positive bone scan rates in initial clinical stage I, II, III and IV were 0%, 4%, 14% and 53%, respectively. 2) The higher clinical stage is, the more cumulative risk of conversion to positive bone scan is during the same follow up period. 3) Conversion rate to positive bone scan in patients with lymph node metastasis is higher (50%) than those without metastasis (18%) (P < 0.001). We concluded that the bone scan in primary breast cancer was very useful to evaluate initial clinical stage and to perform the follow up examination.