BACKGROUND. Preoperative staging of localized extremely soft tissue sarcoma (STS) includes tumor grade, size, and depth. A positive microscopic margin (PMM) adds prognostic information postoperatively, which is not helpful for preoperative stratification into low and high risk groups. This study was undertaken to identify molecular markers associated with poor outcome that could be used to refine the preoperative staging of high grade extremity STS. METHODS. Between January 1, 1983, and December 31, 1989, 1416 patients were entered into the STS prospective data base at the Memorial Sloan-Kettering Cancer Center. Of 232 patients identified with primary, high grade extremity lesions, 121 had tissue available for immunohistochemical (IHC) analysis. The clinicopathologic variables and molecular markers for the original 232 patients were correlated with those for the 121 patients analyzed in the current study. Overexpression of Ki-67, p53, and mdm2 and deletion of Rb were determined via standard IHC techniques on serial paraffin sections. Categoric overexpression was defined as ≤20% nuclear staining. Continuous determination of the percentage of nuclear staining was also used for correlation with distant metastasis (DM) and tumor mortality (TM). Univariate and multivariate analyses were conducted with log rank and Wilcoxon tests and Cox regression analyses, respectively. RESULTS. The median follow-up was 64 months. Fifty-four of the 121 patients (45%) developed DM. Fifty-one of the 121 patients (42%) died of their disease. Factors found to be significant in univariate and multivariate analyses for both DM and TM were Ki-67 score, size, and PMM (all P values <0.05). Five year freedom from DM with a Ki-67 score of <20 was 70% versus 50% for a score. Overexpression of p53 of mdm2 or deletion of Rb did not correlate with increased risk of DM or TM alone or in combination with a Ki-67 score of ≤20. CONCLUSIONS. In addition to standard preoperative criteria, Ki-67 score is an independent prognostic molecular marker that predicts DM and TM in high grade extremity STS. Selecting patients with high grade tumors for preoperative investigational treatment may be further refined according to whether the patients have Ki-67 score of ≤20 and large tumor size.