To study the sonographic (US) evolution of hepatocellular carcinoma, 53 tumors in 45 untreated patients were observed regularly with real-time US for a period of 6 to 56 months. At the beginning, 25 tumors were hypoechoic, 18 isoechoic, 4 hyperechoic, and 6 had mixed hypo/hyper echo patterns. At the follow-up, 7 initially hypoechoic tumors had changed to hyperechoic or to mixed echo patterns; 8 hypoechoic tumors had become isoechoic; 9 of the 25 initially hypoechoic neoplastic lesions had maintained the same echo density. Ten of the 15 initially isoechoic tumors had changed to mixed echo patterns, and 5 had remained unchanged. Three initially isoechoic lesions and a hypoechoic one had turned into diffuse patterns; 2 initially hyperechoic neoplastic lesions had remained unchanged; 1 had switched into hypoechoic, and 1 changed to mixed echo pattern; 4 out of 6 tumors with echo pattern had remained unchanged, 1 had become hyperechoic and 1 hypoechoic. The current study has proven various tumors less than or equal to 3 cm phi to be isoechoic, and most tumors greater than 3 cm phi to have mixed hypo/hyper echo patterns. The echogenicity of small hepatocellular carcinomas increases with the tumor growth, and remains unchanged when they do not increase in size.