We have observed two types of paucity of interlobular bile ducts (PILBD) in children with chronic cholestasis: the syndromic type, which is more frequent (80 cases), and the nonsyndromic type (31 cases). Study of patients with syndromic PILBD has enabled us to recognize five major features: peculiar facies (95%), chronic cholestasis (91%), posterior embryotoxon (88%), butterfly-like vertebral arch defects (87%), and peripheral pulmonary artery hypoplasia or stenosis, either isolated or associated with complex cardiovascular abnormalities (85%). By observing these major features, it is possible to differentiate the "complete" syndrome, in which all five features are present (26 cases), from the "partial" syndrome, in which only four (42 cases) or three (12 cases) major features are present. Other less frequent features were observed in patients with complete or partial syndrome: growth retardation (50%), mental retardation (16%), renal disturbances, other vascular malformations, bone abnormalities, high-pitched voice, and delayed puberty. Death occurred in 21 (26%) patients with syndromic PILBD. Therapy consisted of supplementation of medium-chain triglycerides and fat-soluble vitamins and administration of cholestyramine or phenobarbital. An autosomal dominant mode of transmission, with variable penetrance, seems likely.