We prospectively screened for liver disease patients with cystic fibrosis who were more than 3 years of age and who were followed at the cystic fibrosis center of the University of Milan. From January 1991 to December 1992, we screened 189 patients; clinical, biochemical, and echographic abnormalities suggestive of overt liver disease were present in 34 (18%). To define risk factors for the development of liver disease associated with cystic fibrosis, we evaluated the possible role of specific mutations of the CFTR (cystic fibrosis transmembrane regulator) gene and of different clinical and demographic characteristics (sex, pancreatic status, meconium ileus or its equivalent) through a comparison of patients with cystic fibrosis and overt liver disease (n = 34) and those without liver disease (n = 155). Genetic analysis failed to reveal any significant difference in the allele frequencies of defined (delta F508, 1717-1G-A, G542X, N1303K, W1282X, R553X) and undefined mutations of the CFTR gene in the two groups of patients; genotype frequencies were also not significantly different. Pancreatic insufficiency was present in all patients with liver disease and in 87.3% of those without liver disease. A male predominance was found in the group with liver disease. The frequency of meconium ileus or its equivalent was significantly higher in patients with cystic fibrosis and liver disease (35.3%) than in patients without liver disease (12.3%) (p = 0.0025). In the 31 patients with a history of meconium ileus or its equivalent, the following hepatic abnormalities occurred more frequently than in the 155 patients with cystic fibrosis who did not have meconium ileus: hepatomegaly, biochemical abnormalities, heterogeneous echographic pattern of the liver, and microgallbladder. Twenty-four patients with a history of meconium ileus or its equivalent underwent hepatobiliary scintigraphy (with technetium-labeled iminodiacetic acid derivatives), which showed morphologic abnormalities suggestive of impaired biliary drainage in 21 patients and abnormalities in function in 11. The risk of acquiring liver disease was increased almost fourfold in patients with a history of meconium ileus or its equivalent, in comparison with patients who had cystic fibrosis but were unaffected by these complications (odds ratio, 3.9043; 95% confidence interval, 1.666 to 9.149). We conclude that patients with cystic fibrosis and meconium ileus or its equivalent may benefit from prophylactic treatment with ursodeoxycholic acid; genetic analysis of the major mutations present in this population failed to provide evidence of the existence of a specific genetic marker for the development of liver disease in patients with cystic fibrosis.