The purpose of this study was to investigate the natural history of adenomatous hyperplasia (AH) in liver cirrhosis, which is suspected of being a precancerous condition of hepatocellular carcinoma (HCC). Sixteen patients with 19 histologically proven AH nodules were followed-up over time with ultrasonographic (US) examinations performed every 3-4 months. The biopsy was repeated whenever the volume of the lesion increased, its US pattern changed, or there was a change in the alpha-fetoprotein values. Thirteen out of 19 AH (68.4%) evolved toward HCC after 8-31 months (mean 14.2 months). Malignant transformation was proved in 7/18 AH within 1 year of its initial detection, in 12/15 AH within 2 years, and in 13/14 AH within 4 years. Six AH remained unchanged in size and US pattern for 9-70 months (mean 29.5 months). Long term follow-up of AH confirms that this lesion is a precursor of HCC.