Five to 15% of patients with primary sclerosing cholangitis (PSC) develop cholangiocarcinoma (CC) with a median survival of 5 to 7 months, an outcome not significantly improved by liver transplantation. However, if CC is found incidentally during the procedure or in the explanted liver, 5-year survival rates of 35% are reported. A noninvasive method to detect CC small enough to allow for intended curative surgery is needed. Unfortunately, computed tomography (CT) and ultrasonography (US) have poor sensitivity for detection of CC in PSC; however, positron emission tomography (PET) using 2-[F-18]fluoro-2-deoxy-D-glucose (FDG) differentiates well between CC and nonmalignant tissue. We examined whether PET findings are valid using a blinded study design comparing pretransplantation FDG-PET results with histology of explanted livers. Dynamic FDG-PET was performed in 24 consecutive patients with PSC within 2 weeks after listing for liver transplantation and with no evidence of malignancy on CT, magnetic resonance imaging, or ultrasonography. The PET Center staff was blinded to clinical findings, and surgeons and pathologists were blinded to the PET results. Three patients had CC that was correctly identified by PET. PET was negative in I patient with high-grade hilar duct dysplasia. In 20 patients without malignancies, PET was false positive in I patient with epitheloid granulomas in the liver. In conclusion, dynamic FDG-PET appears superior to conventional imaging techniques for both detection and exclusion of CC in advanced PSC. FDG-PET may be useful for screening for CC in the pretransplant evaluation of patients with PSC.