We studied the usefulness and the limits of the ultrasonic diagnostic criteria for liver tumours formulated by the Japan Society of Ultrasonics in Medicine (JSUM). 226 cases with liver mass lesions were enrolled in this study. At least one of the criteria reached a value of over 80% for one of the items: sensitivity, specificity, positive predictive value, negative predictive value or overall accuracy. In the differentiation of liver tumours, sharp & smooth boundary, presence of marginal hypoechoic zone, mosaic pattern, starry anechoic area, posterior echo enhancement and lateral shadows were important for HCC. For metastatic liver cancer, potato shape, coarsely irregular boundary, presence of marginal hypoechoic zone, internal target like anecho were important features. The liver pathology of the false negative cases corresponded to: a) liver tissue completely replaced or infiltrated by HCC or metastasis. b) the non-tumour tissue and tumour tissue were isoechoic but also without marginal hypoechoic zone. c) the ultrasonograms of non tumoural areas were modified by calcification of eggs of schistosomiasis and severe fibrosis. It can be concluded that most HCC and metastatic liver cancers over 3 cm in diameter can be diagnosed correctly by the JSUM's criteria. However, complimentary image diagnosis and fine needle biopsy are important to assure the highest diagnostic score in cases with US negative and small tumours.