OBJECTIVE: In this study, we aimed to identify prognostic factors in anaplastic hemangiopericytoma (AHPC) and clinical behaviors that differentiate primary and secondary AHPC. METHODS: The clinical data associated with 52 cases of AHPC that were surgically treated between 2008 and 2015 were reviewed. The patients were classified into the following 2 groups: primary AHPC (AHPC diagnosed at the first surgery) and secondary AHPC (malignant transformation from a lower-grade tumor). RESULTS: The study included 27 men and 25 women. The participants had a mean age of 43 years old. The 3-and 5-year progression-free survival (PFS) rates were 63.4% and 53.5%, respectively, and the corresponding overall survival rates were 78.7% and 70.9%, respectively. At the final follow-up, there were 22 (42.3%) recurrences, 4 (7.7%) extracranial metastases, and 11 (21.2%) deaths. On the basis of multivariate analysis, primary AHPC (hazard ratio [HR] = 0.293, 95% CI 0.122-0.705) and postoperative radiotherapy (PRT) (HR = 0.372, 95% confidence interval [CI] 0.148-0.932; P = 0.035) were significantly associated with increased PFS, and gross total resection (HR = 3.512, 95% CI 1.060-11.634; P = 0.040) and PRT (HR = 0.165, 95% CI 0.035-0.771; P = 0.022) were independent favorable factors for overall survival. CONCLUSION: Gross total resection and PRT following surgery are recommended in AHPC. Identifying clinical behaviors that differentiate primary and secondary AHPC