BACKGROUND : To describe the clinicopathological features of primary retroperitoneal solitary fibrous tumor (RSFT) and define the prognostic factors. METHODS : The comprehensive data of 35 primary RSFT patients who got curative surgery at a tertiary cancer center from April 2004 to October 2018 were retrospectively analyzed. RESULTS : Male patients outnumbered female patients (19 vs. 16), with the age ranging from 19 to 73 years (median, 51 years). 7 (20%) patients had tumors located in special parts, including three in kidney, one in renal pelvis, one in bladder, one in prostate, and one in mesentery. Tumor sizes ranged from 2.5 to 25 cm (median, 9 cm). Microscopic negative margin was reached in 33 (94.3%) cases. 13 (37.1%) were classified as atypical/malignant, while 22 (62.9%) were benign. Concomitant organ excision was performed on 11 (31.4%) patients, with kidney (n = 5) being the most frequent organ. Multifocality was only found in 4 (11.4%) cases. The majority of the patients (31, 88.6%) did not get adjuvant treatment. The median follow-up time was 46 months (range 4-153 months). The 5-year DSS rate and DFS rate were 100% and 63.6%, respectively. In univariate analysis, tumor size ≥ 10 cm (P = 0.002) and atypical/malignant pathology (P = 0.024) were associated with decreased DFS. Multivariate analysis revealed that tumor size was the only independent prognostic factor for DFS (HR 6.03, 95% CI 1.18-30.77, P = 0.031). CONCLUSIONS : RSFT is uncommon, slow-growing, and recrudescent tumors. Large tumor size and malignant pathology are associated with decreased DFS. Tumor size ≥ 10 cm independently predicts shortened DFS.