The clinical manifestations of hepatocellular carcinoma (HCC) are highly nonspecific since they usually mimic those of hepatic cirrhosis, which frequently underlies this neoplasm. The fact that some HCC patients present with severe diarrhea, an unusual symptom in liver cirrhosis, prompted us to determine the prevalence of diarrhea in a series of 23 consecutive HCC patients and compare it with that of a control group formed by cirrhotic patients without HCC, matched by age, sex, and etiology of the liver disease. All the patients were interviewed about the existence of diarrhea (defined as the presence of three or more loose stools per day appearing over three or more days) in the three months prior to admission. Both groups of patients were similar in regards to the degree of liver failure and presence of diarrhea-favoring factors. By contrast, diarrhea was significantly more frequent among HCC cases than among cirrhotics without HCC (47.8% vs 8.7%, P less than 0.005). HCC patients with diarrhea exhibited higher alkaline phosphatase and bilirubin levels and worse liver function, assessed by the Child-Pugh's classification, than patients without diarrhea. However, neither tumor size, vascular invasion, or the degree of tumor differentiation were significantly different between these two groups of HCC patients. These results show that diarrhea is a frequent manifestation of HCC in patients with cirrhosis. Therefore, the development of HCC in these patients should be suspected upon the appearance of diarrhea.