The significance of large cell dysplasia and small cell dysplasia as premalignant lesions has been extensively discussed. At present the majority of researchers consider that the former seems to be a secondary change rather than a premalignant lesion, and the latter is strongly suggested to be a premalignant lesion. In the past decade, however, adenomatous hyperplasia (dysplastic nodules), the nodular lesions seen in the cirrhotic liver, has attracted researchers' interest. The significance of adenomatous hyperplasia as a premalignant lesion has been supported by its frequent occurrence in the vicinity of hepatocellular carcinomas (HCC), the presence of adenomatous hyperplasia containing distinct cancerous foci, frequent malignant transformation seen in follow-up studies, and so forth. For histological diagnosis of adenomatous hyperplasia, a thorough understanding of the pathology of well-differentiated HCC at an early stage is essential. Reports from Europe and the United States on dysplastic nodules often include well differentiated HCC at the early stage, possibly because of the lack of opportunity for Western pathologists to see minute early-stage well differentiated HCC. In addition, Western pathologists usually have no concept of "carcinoma in situ" in which no obvious invasive growth is present, and many cases of gastric cancer in the mucosa are diagnosed as dysplasia in Europe and the United State.