Radiation induced sarcomas offer diagnostic and therapeutic challenges. The authors report an unusual case of radiation induced sarcoma arising 9 years after radiation therapy for chordoma. The location of this mass in the retroperitoneum and its intimate involvement with the spine raised difficult management issues. After limited resection was performed, consistent with the intraoperative diagnosis of a benign neurofibroma, foci of malignant transformation were found in areas of the specimen remote from the biopsy site. This complicated management of the sarcoma. The possibility of occult malignancy should be considered when evaluating tumors arising in a previously irradiated field. Thorough sampling at the time of biopsy is required to evaluate such lesions, particularly peripheral nerve sheath tumors.