An 11-year-old boy was treated since 6-years-old with methylphenidate for combined attention deficit and hyperactivity disorder. At age nine his behaviour had worsened and he started to have phobias. One year later persistent hypertransaminasemia was found. Physical examination showed a dysdiadocokinesia. Laboratory investigation revealed a low caeruloplasmin and augmented basal urinary copper with a positive postpenicillamine test. Liver biopsy showed high liver copper (853 µg/g) and brain MRI was normal. D-penicillamine and zinc acetate were started without side effects. ATP7B gene mutation was confirmed after treatment initiation.