A 41/2-year-old asymptomatic girl with persistent elevated serum transaminase levels for eight months was found to have Wilson's disease. The diagnosis was suspected by the presence of fatty liver and nonspecific chronic hepatitis on liver biopsy and was proved by studies of copper metabolism, including determinations of serum ceruloplasmin and hepatic copper concentrations. Unexplained persistent transaminase elevation in children demand investigation by needle liver biopsy. Th presence of fatty liver and hepatitis should raise the possibility of Wilson's disease, which may then be confirmed by more specific tests. Advantages to early diagnosis include the institution of specific therapy and prevention of progressive liver disease.