Objective To testify the efficacy of 18F-fluorodeoxyglucose（18F-FDG） positron emission tomo-graphy（PET） in the diagnosis of cancer.Methods A total of 170 patients with diagnosed cancer or suspicious cancer were enrolled in this study

and underwent 18F-FDG PET.The standard uptake value（SUV） and diameter for each abnormal region in PET images were analyzed.All data were analyzed by SPSS 11.5.Results PET scan identified a primary cancer in 45.8%（11/24） patients.The sensitivity and specificity of PET scan in differentiating malignant lesions from benign ones were 78.8%（52/66） and 77.1%（27/35） respectively.Twenty-nine out of 68（42.6%） lesions were detected earlier by PET than by computed tomography.The SUV of primary cancer was significantly higher than that of metastatic lymph nodes（5.84±3.12 vs.3.14±2.24

P<0.001）.And SUV of primary lung cancer was also significantly higher than that of metastatic lung cancer（6.30±3.01 vs.2.86±2.37

P<0.01）.Conclusion 18F-FDG PET plays a very important role in cancer diagnosis.