We have attempted to evaluate the role of preoperative and postoperative bone scans in patients with localized carcinoma of the breast. The yield of positive preoperative scans in patients with Stages I and II disease is low and confounded by a relatively high percentage of false-positive results. Conversely, 16 per cent of patients with Stage III disease had evidence of bony metastasis at the time of operation. Positive bone scans were found three times as frequently in patients with axillary node involvement than in those without. Thirty per cent of those observed for varying times up to 41 months had evidence of bony metastases. Again, there was a correlation with initial clinical staging with 3.6 to 8.0 times more conversions in patients with Stage II or III disease than in those with Stage I disease. It appears that the majority of metastases to the bone become apparent within the first years. This observation deserves further study to elaborate the natural history of metastatic carcinoma of the breast.