Prostate cancer is difficult to visualize using current techniques. Recently, 31P magnetic resonance spectroscopy has revealed that the tumor, in general, is characterized by an increased uptake of choline into the cell to meet increased synthesis of phosphatidylcholine, an important cell membrane phospholipid. We succeeded in using 11C-choline to visualize prostate cancer and its local metastasis in PET. METHODS PET was performed on 10 prostate cancer patients from the level of pelvis to the lower abdomen. After transmission scanning, 370 MBq 11C-choline were injected intravenously. The emission scan was performed 5-15 min postinjection. Finally, PET images were displayed so that each pixel was painted by a specified color representing the degree of the standardized uptake value (SUV). The 11C-choline image was compared with the 18F-fluorodeoxyglucose (FDG) image obtained from the same patient. RESULTS Imaging of prostate cancer and its local metastasis was difficult when 18F-FDG was used because, within the pelvis, the areas of high uptake were concealed by the overwhelmingly abundant radioactivity in urine (in ureters and bladder). By contrast, it was easy when 11C-choline was used because the urinary activity was negligible and tumor uptake was marked. The radioactivity concentration of 11C-choline in prostate cancer and metastatic sites was at an SUV of more than three in most cases. The SUV of 18F-FDG was considerably lower than that of 11C-choline. CONCLUSIONS Prostate cancer and its local metastasis were visualized clearly in PET using 11C-choline.