Hepatocellular carcinomas (HCCs) are currently treated with surgery, transcatheter chemoembolization and percutaneous alcoholization; all methods require accurate in vivo anatomopathology of the lesion. The authors report their personal experience with 58 HCCs on cirrhosis which were studied with dynamic single-slice CT after the injection of water-soluble iodate contrast medium with automatic injector in a peripheral vein. Three semiologic patterns were identified according to lesion density on pre- and post-contrast images. The active portion of the lesion could be differentiated from the necrotic one in 100% of cases. Moreover, the necrotic lesion was differentiated from possible still viable tumor portions but with vacuolar degeneration phenomena. These findings allowed the authors to calculate the growth rate and the infiltrative capability of the single neoplastic masses. Finally, the dynamic evaluation of parenchymal enhancement allowed abnormal tissue vascularization due to arterioportal communication to be demonstrated in 7 cases. The authors conclude the dynamic single-slice CT allows the accurate assessment of HCC foci, of tumor tissue vascularization and of perilesional liver parenchyma. Therefore, dynamic single-slice CT is suggested as the technique of choice to study small HCCs before treatment.