Abstract: Objective :To retrospectively analyze the clinical value of detecting primary tumorswith ¹⁸F-FDG PET/CT whole body imaging. Methods :Thirty-three patients with cancers of unknownprimary (CUP) sites underwent ¹⁸F-FDG PET/CT whole body imaging. The primary tumors and metas-tases were detected by visual evaluation and measurements of standardized uptake values (SUVs).Thefinal results were confirmed with clinical follow-up or more comprehensive analysis. Results :Primarytumors were confirmed with ¹⁸F-FDG PET/CT whole body imaging in 25/33 (75.8%) cases. Among the25 cases whose primary tumors were confirmed, 9 had tumors in the lung, 2 had tumors in the liver, 2had tumors in the nasopharynx, and 2 had tumors in the thyroid. The remaining tumors were found inthe breast, esophagus, stomach, pancreas, intestinal tract, kidney, prostate gland, brain, lymphatic sys-tem, and blast cells in the retroperitoneum. Conclusion :¹⁸F-FDG PET/CT whole body imaging effec-tively finds primary tumors in patients with CUP.The distribution of lesions can be clearly reflected inthe whole body by one scan,a feature that has important clinical significance for selecting appropriatetherapeutic methods and evaluating prognosis.