The median age of the population with cystic fibrosis (CF) has increased worldwide, which has led to the suggestion that the prevalence of liver disease would increase. The aim of this study was to evaluate the natural history of CF-associated liver disease over a 15-year period in a well-controlled population of patients with CF. During the years 1976 through 1993, 124 patients were followed up by yearly liver function tests (LFTs). Fifteen patients were followed up with liver biopsies throughout the whole study period. More than 50% of the patients had pathological LFTs in infancy, later being normalized. Approximately 25% of children 4 years of age or older had biochemical markers of liver disease during the study period. In about 10% of the patients, cirrhosis or advanced fibrosis was confirmed at biopsy and 4% of patients had cirrhosis with clinical liver disease. Severe liver disease developed mainly during prepuberty and puberty. Of the 15 patients prospectively followed up with liver biopsies, only 3 had progressive fibrosis. No specific risk factor was identified, but deficiency of essential fatty acids was found more often in patients with marked steatosis (P <.05). No patient developed clinical liver disease in adulthood and the histological changes in the liver biopsies were usually not progressive. Liver disease was no more frequent at the end of the study period although the median age of the patient population had increased. Modern treatment might positively influence liver disease because it seemed less common, less progressive, and less serious than previously reported.