Clonorchiasis is a snail-transmitted trematodiasis caused by Chinese liver fluke, Clonorchis sinensis. Forty-two patients with the disease were examined with CT. Seventeen patients had clonorchiasis alone, and 25 patients had clonorchiasis with hepatobiliary malignancies (20 cholangiocarcinomas, four hepatocellular carcinomas, one carcinoma of the ampulla of Vater). In three of the 17 patients with clonorchiasis alone, the CT scans were normal. In 14 patients (82%), CT showed diffuse, minimal, or mild dilatation of the intrahepatic bile ducts. None of the patients had marked dilatation. The extrahepatic biliary tree was normal in all 17 patients. All 25 patients with clonorchiasis and hepatobiliary malignancies had diffuse dilatation of the intrahepatic bile ducts on CT, including 18 patients with minimal or mild dilatation and seven patients with marked dilatation. All seven patients with marked dilatation had extrahepatic biliary malignancies. Clonorchis sinensis per se or thickening of the bile duct wall could not be recognized on CT scans. Additional abnormalities evident on CT included pyogenic liver abscesses in two patients and gallstones in five patients. The diagnosis of clonorchiasis can be suspected when CT shows diffuse, uniform, and minimal or mild dilatation of the intrahepatic bile ducts, particularly in the periphery of the liver, without evidence of extrahepatic biliary dilatation.