Intrathoracic solitary fibrous tumor (SFT) is a rare disease. Radical resection is the standard of care. However, estimating prognosis and planning follow-up and treatment strategies remains challenging. Data were retrospectively collected by five international centers to explore outcome and biomarkers for predicting event-free-survival (EFS). 125 histological proven SFT patients (74 female; 59.2%; 104 benign; 83.2%) were analyzed. The one-, three-, five-and ten-year EFS after curative-intent surgery was 98%, 90%, 77% and 67%, respectively. Patients age (>= 59 vs.<59 years hazard ratio (HR) 4.23, 95 confidence interval (CI) 1.56-11.47, p=0.005), tumor-dignity (malignant vs. benign HR 6.98, CI 3.01-16.20, p<0.001), tumor-size (>10 cm vs.<= 10 cm HR 2.53, CI 1.10-5.83, p=0.030), de Perrot staging (late vs. early HR 3.85, CI 1.65-8.98, p=0.002) and resection margins (positive vs. negative HR 4.17, CI 1.15-15.17, p=0,030) were associated with EFS. Furthermore, fibrinogen (elevated vs. normal HR 4.00, CI 1.49-10.72, p=0.006) and the neutrophil-to-lymphocyte-ratio (NLR >5 vs.< 5 HR 3.91, CI 1.40-10.89, p=0.009) were prognostic after univariate analyses. After multivariate analyses tumor-dignity and fibrinogen remained as independent prognosticators. Besides validating the role of age, tumor-dignity, tumor-size, stage and resection margins, we identified for the first time inflammatory markers as prognosticators in SFT.