Idiopathic adulthood ductopenia (IAD), named only 10 years ago, is the latest entity to join the group of small-duct biliary diseases. On the basis of published data and my consultation practice, I am aware of 57 cases. Most commonly, IAD affects young or middle-aged adults (overall range of affected patients, 15 to 77 years) and occurs with a distinct male preponderance. The median age of male and female patients among 48 published and unpublished cases was 30 and 36 years, respectively (in 9 cases, the precise age had not been stated). The age range probably encompasses several etiologic groups with different age distributions. Biopsy specimens, by definition, show ductopenia and its complications but no other lesions. Laboratory studies reveal a cholestatic profile, but again, by definition, these cases show no changes that would be diagnostic or suggestive of another biliary disease. In approximately half the published cases in which the outcome was reported, the condition seemed to have a benign course; in contradistinction, the other cases of IAD were fatal or necessitated liver transplantation. Indirect evidence suggests that IAD is a syndrome with several causes, including (1) late-onset nonsyndromic paucity of intrahepatic bile ducts, (2) small-duct primary sclerosing cholangitis ("pericholangitis") without large duct involvement and without evidence of inflammatory bowel disease, (3) nonsuppurative viral cholangitis--for instance, in hepatitis C, and (4) autoimmune cholangitis or cholangitis in autoimmune hepatitis, in the absence of the typical autoantibodies (cryptogenic chronic hepatitis). For progressive cases of IAD, liver transplantation is necessary, whether or not a specific cause is suspected.