In a patient who presented with an osteosarcoma of the proximal humerus, systemic staging revealed a lesion in the contralateral humerus, which was shown to be an enchondroma after open biopsy. The patient had a local recurrence develop, which necessitated forequarter amputation. Shortly thereafter, the patient had pain develop at the contralateral biopsy site, and examinations and repeat biopsy revealed metastatic osteosarcoma. We think it is likely that surgical trauma contributed to the development of this unusual metastasis. In this clinical situation, consideration should be given to doing the biopsy and definitive resection on separate occasions.