In ninety families with at least one proven case of Wilson's disease, seen over 32 years, all close relatives were examined and “presymptomatic” disease was diagnosed in 30.11 had one or more abnormal physical signs when examined and 7 of these had Kayser Fleischer rings. In a further 10 patients the abnormalities of copper metabolism were so pronounced as to leave no doubt as to the diagnosis. 6 patients were not seen until they had been on treatment for 2 years or more; in some, much of the evidence on which the diagnosis was based is not available. In 3 patients there were only minor histological abnormalities in the liver and no increase in urinary copper but other indices of copper metabolism pointed to a diagnosis of Wilson's disease. 2 patients had transient neurological signs after starting treatment; otherwise, all but one (who died in an accident) have remained well for up to 26 years.