Ultrasonographic screening and follow-up of patients with chronic liver disease lead to the detection of a large number of small asymptomatic hepatocellular carcinomas, so that the changing appearance of this neoplasm during its natural history has now been recognized. Ultrasonography provides information on shape, echogenicity, growth pattern and vascular involvement of the neoplasm. Three different shapes may be identified, depending upon the size and the invasiveness of the neoplasm: nodular, massive and diffuse. The echogenicity is variable and the tumour mass may appear hypo, hyper or isoechoic in comparison with the surrounding liver tissue. A mixed pattern and/or a hypoechoic ring may also be visualized. A tendency to change from a low echo pattern to a low periphery and finally to a massive pattern with increasing echogenicity has been shown in Japanese patients. The infiltrative growth pattern may be grossly distinguished from the expansive one on the basis of the aspect of the tumour boundary. Vascular invasion is easily recognizable as a mass within a major portal branch or even in the portal trunk. Duplex and color Doppler ultrasonography enable further insights on the vascular alterations related to this neoplasm. Abnormal signals, typical of HCC, are characterized by high-peak with broadening of spectrum. Low impedance continuous signals are less characteristic. Finally, ultra-sound guidance allows puncture of intrahepatic nodules as small as 1cm. The sensitivity of this procedure in the diagnosis of focal liver lesions is very high, varying between 91% and 95% with a specificity of 92%-100%.