The aim of this study was to investigate the role of F-18 fluoro-2-deoxyglucose positron emission tomography/computed tomography (F-18 FDG PET/CT) in diagnosis and prognostic evaluation of secondary hemophagocytic syndrome (HPS). A total of 11 secondary HPS patients examined with 18F-FDG-PET/CT were retrospectively analyzed. The diagnostic value of F-18 FDG PET/CT for malignancy detection was assessed. The values of maximum standardized uptake value (SUV(max)) in spleen (SUVS(p)) and in bone marrow (SUVBM) were measured to analyze their relationship with various laboratorial parameters and clinical outcome of secondary HPS patients. The results showed that 4 out of the 11 patients had malignancies, the sensitivity, specificity and diagnostic accuracy of F-18 FDG PET/CT for malignancy detection were 100%, 66.7% and 75% respectively, the SUV(max) of spleen and bone marrow showed no significant correlation with laboratorial parameters, a maximum SUVS(p) of 3.10 and a maximum SUVBM of 3.47 were the optimal cutoffs for predicting patients' outcome, the increased uptake of F-18 FDG in the BM and spleen were significantly associated with shorter survival time according to univariate analysis. It is concluded that 18F-FDG PET/CT may especially play an important role in diagnosis and predicting outcome of secondary HPS for the small sample size.