In connection with 6 cases of Wilson's disease, the authors recall the main features of this hereditary metabolic disorder at late onset (usually the second decade), treatable with a chelating agent, when diagnosed at an early stage. Wilson's disease is first of all a liver disease and the authors emphasize the fact that cirrhosis is usually present when neurologic symptoms, revealing the disease in 5 cases, appear, even if there is no clinical or biological evidence for liver disease. In one instance hemolytic anemia and chronic active hepatitis were observed at clinical onset. Copper metabolism usually gives the key for diagnosis but its interpretation may be difficult, a normal serum ceruleoplasmin level being found in two patients and evaluated at 6% in the literature. This fact brings up the puzzling question of the pathogesis of the disease. Wilson's disease is not a simple ceruleoplasmin synthesis defect, but a lysosomal disease responsible for the lack of copper biliary excretion. This is pointed out by histochemical studies using a special rubeanic acid preparation (revealing copper deposit on the biliary side of the hepatic cell), and by electron microscopy showing lysosomal dystrophy.