Abstract: Objectives To evaluate the diagnostic capability of 18F-FDG PET/CT in differentiating benign from malignant pancreaticcystic lesions. Methods Between July 2008 and March 2016, all patients with pancreatic cystic lesions that had 18F-FDG PET/CT were reviewed. The sizes and maximum standardized uptake values（SUVmax） of the pancreatic cystic lesions were measured. The definition of the gold standard was based on histopathologic findings（n=52） and operative findings without biopsy（n=1） and percutaneous biopsy（n=2）. All statistical analyses were performed using SPSS 19.0. Results A total of 55 patients with pancreatic cystic lesions were enrolled for the study. Of all patients, 29 had benign lesions but 26 were assigned to the malignant group （23 with malignant neoplasms, 3 with borderline neoplasms）. 18 patients had cystic lesions that were smaller than 3 cm in diameter （8 with malignant neoplasms, 10 with benign lesions）, and 37 patients had cystic lesions 3 cm in diameter or bigger（18 with malignant neoplasms, 19 with benign lesions）. For lesions that was smaller than 3 cms in the diameter, SUVmax between malignant and benign lesions were of no statistical difference（2.91±2.08） vs. （2.48±1.10）, P=0.601. For lesions that was 3 cm in the diameter or bigger, SUVmax was significantly higher in malignant than in benign lesions（2.71±2.06） vs. （6.56±3.95）, P=0.001. The optimal cut off value of SUVmax for differentiating benign from malignant pancreatic cystic lesions was 3.0, which was determined by receiver-operating- characteristic analysis using the highest Youden index. For all of the lesions, sensitivity, specificity, positive and negative predictive values, and accuracy of 18F-FDG PET/CT indetecting malignant cystic lesions were 65%, 79%, 74%, 72% and 73%, respectively. For 37 lesions that was 3 cm s in the diameter or bigger, sensitivity, specificity, positive and negative predicti vevalues, and accuracy of 18F-FDG PET/CT indetecting malignant cystic lesions were 89%, 84%, 84%, 89% and 86%, respectively. Conclusion 18F-FDG PET/CT is an accurate imaging modality for differentiating between benign and malignant pancreatic cystlesions that were 3 cm in the diameter or bigger, and which is not accurate for lesions that were smaller than 3 cm in the diameter.