BACKGROUND Increased tumor neovascularity has been shown to correlate with poor prognosis in solid tumors. METHODS Microvessels were identified by factor VIII immunohistochemical staining. Analysis of microvessel counts, tumor characteristics, and resection details was performed on 119 primary, high-grade extremity soft tissue sarcomas (STS) and correlated with clinical outcome. RESULTS Tumor characteristics and resection details were analyzed and patient outcome was examined with respect to local recurrence, distant metastasis, and disease-specific survival. Factors found to be significant on univariate analysis for all outcome variables were positive microscopic margin and tumor size. A positive microscopic margin was found to be a significant risk factor for local recurrence (P = .03), distant metastasis (P = .006), and disease-specific survival (P = .004). A primary tumor greater than 10 cm in diameter was a poor prognostic factor for distant metastasis (P = .03) and disease-specific survival (P = .006) when compared to tumors smaller than 10 cm. Microvessel count did not correlate with survival nor did it predict distant metastasis or local recurrence. Histologic subtypes of STS that have a prominent vascular pattern as a diagnostic criterion (i.e., angiosarcoma, liposarcoma, hemangiopericytoma) form a subgroup of all STS. Neovascularity in these subtypes showed no relationship to clinical outcome. CONCLUSIONS These data confirm the prognostic importance of microscopic margin and tumor size in high-grade extremity STS. Neovascularity measured by factor VIII staining had no prognostic significance in these mesenchymal tumors, in contradistinction to carcinomas. Alternatively, microvessel counts may not accurately represent the angiogenic capacity of STS. Therefore, patients with STS who are eligible for anti-angiogenesis clinical trials cannot be identified solely by microvessel count.