To assess the prevalence, demography, and clinical features of liver disease among patients with cystic fibrosis the case notes of 524 patients of all ages who were attending the cystic fibrosis clinic were studied. Computer databases were used to establish the condition of the liver in a further 576 such patients. The overall prevalence of overt liver disease indicated by the presence of an enlarged liver or spleen (or both) was 4.2%. The age related prevalence rose to a peak in adolescence, and then fell in patients over 20 years old. The implied increase in mortality among those with liver disease was not explained by deaths from liver disease, which were rare. Male patients were significantly more affected than female, the ratio being 3:1 among adolescents. Increasing prevalence of liver disease in patients with cystic fibrosis is, therefore, not just a result of longevity.