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The causes of cholestasis in 276 patients with a total of 296 lesions were studied. Extrahepatic cholestasis was found in 58.4 percent of the patients, and 41.6 percent had intrahepatic cholestasis. Malignant disease was found in 34.8 percent of the patients (extrahepatic cholestasis in 20 and intrahepatic cholestasis in 70). Cholangiocarcinoma, especially the hilar intrahepatic type, seems to be the most prevalent in the medical literature. It is possible that the combination of opisthorchiasis and carcinogenic agents, such as nitrosamines, induce a precancerous stage at the hilar area. Some unknown factors, may be the immune system in immune surveillance that act as a catalyst leading to malignant transformation. Acute calculous cholecystitis, choledocholithiasis, and intrahepatic stones are more common in Thailand than in the western countries, and their causes have been discussed herein. The composition of stones is also different; pigment stones are found more often in Thailand. These differences between the western and oriental types of biliary calculi are significant in regard to diagnostic approach and management, and morbidity and mortality. In Thailand, Opisthorchiasis viverrini has significant influence in the development of several cholestatic diseases, such as hilar intrahepatic cholangiocarcinoma, biliary calculi, opisthorchiatic intrahepatic cysts, and aggregated dead opisthorchiatic worms blocking the biliary system. In tropical countries, infectious diseases such as virus B hepatitis; severe systemic infectious diseases such as salmonellosis; and amebiasis and tuberculosis were also important causes of intrahepatic cholestasis. In the category of congenital anomalies, the prevalence of choledochal cysts was higher than in the United States. The prevalence of other forms of congenital anomalies of the biliary system is unknown, but may be similar to the prevalence of choledochal cysts.