The evaluation of surgical margin is useful in determining the curability of surgical treatment of musculoskeletal sarcoma and the degree of possibility to reduce later surgery as part of preoperative therapy. However, at present there has been no worthwhile evaluation method developed for these purposes. In this paper we propose a new evaluation system for surgical margin as drafted by the Bone and Soft Tissue Tumor Committee of JOA. This system was applied in 197 cases at the Cancer Institute Hospital to determine the clinical significance in the treatment of musculoskeletal sarcoma. In this method, surgical margin was classified into four types according to the distance between the surgical margin and the reactive zone of the tumor. The types of surgical margins (in order of surgical extent) are curative margin, wide margin, marginal margin, and intralesional margin. Surgical margin is said to be curative if the margin is more than 5cm outside the reactive zone. It is referred to as wide if the margin is less than 5cm and marginal if the margin is at the reactive zone. In our evaluation, a thin barrier is estimated as a 2cm thickness of normal tissue, a thick barrier as a 3cm thickness of normal tissue, and joint cartilage as 5cm thickness. Moreover, in all cases the surgical margin is considered to be curative if the margin is outside a barrier and there is normal tissue between the barrier and the reactive zone of the tumor. The results of the study were as follows.(ABSTRACT TRUNCATED AT 250 WORDS)