We performed this study to evaluate detectability and delineation of extent of hepatocelluar carcinoma bycomparison between nonenhanced and contrast-enhanced CT scan. During a three-year period, 174 patients withhepatocellular carcinomas were examined by CT at Seoul National University Hospital. Fifty-three patients hadhistological proof by operation or liver biospy, while 121 patients were diagnosed by characteristic angiographic finding and elevated alpa fetoprotein level(<500ng/ml). All 174 patients were studied with a CT-9800 scanner. CT scans were obtained both before and after administration of contrast medium. Contrast material was given by bolus injection of 120ml of ioxitalamate meglumine. CT findings were divided into three categories: Good: tumor isnoted, and extent of tumor is clearly defined: Fair: tumor is noted, but extent of tumor is not defined: Poor:tumor is not noted. In 165 cases of the tumor on nonenhanced CT scans, 131 cases (79%) showed low-density, 29 cases(18%) isodensity, one case, high-density and 4 cases(2.4%) mixed density. In 174 cases of the tumor oncontrast-enhanced CT scans, 170 cases (97%) showed low-density, 3 cases(1.8%) iso-density, and 1 cases mixeddensity(0.6%). In 165 cases of the tumor on nonenhanced CT scans, 64 cases (39%) were categorized as good in tumorlocalization, 53 cases(32%) as fair, and 48 cases(2.9%) as poor. However, 174 cases of the tumor oncontrast-enhanced CT scans. Our results indicate that contrast-enhanced CT scans are better than nonenhanced CT scans in detecting the tumor and defining them and reduce radiation exposure to the patients by omittingnon enhanced CT scans in clinically suspected hepatocellular carcinoma.