Several types of biliary tract abnormality of undetermined origin have been described among AIDS patients. The aims of this study are: (1) to evaluate whether biliary tree involvement is in fact one or several homogeneous morphological entities, (2) to specify the role of CMV or Cryptosporidium sp. infection, and (3) to evaluate the possible efficacy of treatment. Since ultrasound had revealed abnormality in the biliary tree, 26 consecutive AIDS patients underwent cholangiography. Cholangiograms enabled us to distinguish between two types of biliary tract involvement: (1) gradual and regular stenosis of the terminal portion of the common bile duct associated with dilation but without irregularity of the intrahepatic biliary ducts was present in 27% of our cases, and (2) distal stenosis of the extrahepatic biliary ducts combined with diffuse irregularity of the caliber of the intrahepatic bile ducts was present in 73% of our cases. Concomitant infection by CMV or Cryptosporidium sp. was significantly more frequent when intrahepatic duct irregularities were present (94%) than when absent (14%, P < 0.001). Anti-CMV treatment and sphincterotomy were unsuccessful in treating anomalies of the intrahepatic biliary tract. Conversely, sphincterotomy caused rapid and lasting disappearance of pain in all our patients. In conclusion, biliary tract involvement in AIDS patients is of two types. CMV infection and infection by Cryptosporidium sp. are most frequent when the large intrahepatic ducts are implicated.