Prognostic factors associated with local recurrence, metastases, and tumor-related death in synovial sarcoma were studied in 51 patients in the Scottish Bone Tumor Registry from 1955 to 1999. In a multivariate analysis, the presence of poorly differentiated (PD) areas was the strongest prognostic factor associated with local recurrence (Hazard ratio [HR] = 11.3, 95% CI 2.3, 122.5, p = 0.033), metastases (HR = 16.9, 95% CI 2.3,122.5, p = 0.005), and tumor-related death (HR = 6.9, 95% CI 1.1,41.8, p = 0.036). Other significant independent risk factors included bone invasion (HR = 16.6, 95% CI 1.1, 252.5, p = 0.043) and necrosis (HR = 5.1, 95% CI 1.4, 18.99, p = 0.016) for metastases and bone invasion (HR = 17.6, 95% CI 1.2, 253.2, p = 0.035) for tumor-related death. Increasing percentages of PD areas and necrosis were associated with increasing hazard ratios for metastases and death. In the univariate analysis, PD areas, tumor size, and a mitotic count over 10/10 high-power fields were significantly associated with recurrence, whereas necrosis, vascular invasion, and age more than 25 years were additional risk factors for metastases and death. Local recurrence was significantly associated with increased risks for metastases (OR = 6.8, 95% CI 1.6, 28.7, p = 0.006), and death (all cases). Histologic features such as PD areas, necrosis, vascular invasion, and bone invasion should be considered when deciding about adjuvant therapy.