The population of Northeast Thailand has one of the highest known rates of cholangiocarcinoma (cancer of the bile ducts). We sought firstly to obtain an estimate of the frequency of hospital-based diagnosis of cholangiocarcinoma in the northeastern province of Khon Kaen. All pathology, ultrasound and in-patient and out-patient records were searched for cases diagnosed in tertiary hospitals in a random calendar month in 1988. A total of 203 persons from various parts of northeastern Thailand were newly-diagnosed in the two hospitals, 75 of whom resided in Khon Kaen province. We estimated the minimal age-standardised annual incidence rate in this province to be 135.4 per 100,000 among males and 43.0 per 100,000 among females (world standard). Truncated standardised incidence rates (ages 35-64 years only) were 334.2 and 104.3 per 100,000 for males and females respectively. Secondly we aimed to assess the feasibility of secondary prevention by early clinical diagnosis. However, the symptoms and signs observed were typically non-specific and associated with advanced disease in patients with cholangiocarcinoma who presented to hospital. Primary preventive measures appear to be the key to decreasing the mortality from this disease.