The aim of this study was to estimate the prevalence of hepatobiliary dysfunction in a regional unselected group of ulcerative colitis (UC) patients. Five hundred and thirty-four patients were included in this study. Eighty-one per cent of them had never had abnormal alkaline phosphatase (ALP) values and 72% no abnormal alanine amino-transferase (ALAT) values. Thirty patients (6%) had had ALP values more than twice the normal (> 550 U/L) at least once during their disease. Furthermore, 24 (34%) out of 70 patients with routine liver biopsy at colectomy had changes in their liver histology, 13 (19%) of these also having ALP and ALAT values within normal range. Primary sclerosing cholangitis (PSC) had been diagnosed in 11 (2%) patients. All but one of the PSC patients had had ALP and ALAT values more than twice the normal. Almost 30% of all patients had had abnormalities in their liver biochemistry at least once during their disease. Normal liver biochemistry did not seem to exclude changes in liver histology. Although minor hepatobiliary dysfunction is common in patients with UC, more serious conditions such as PSC were found to occur in only 2% of patients.