We report a case of idiopathic bilateral basal ganglia calcinosis, or Fahr's disease (FD) in a 50 year old patient who developed rapidly progressive behavioural abnormalities and severe neuropsychological impairments, but no movement disorder. Neuropsychological deficits included a severe dysexecutive syndrome, anterograde amnesia, and attentional impairment. Neuropsychiatric features comprised apathy with intermittent disinhibition, anxiety, irritability, frequent mood changes, ritualistic and antisocial behaviour, and psychosis. Fluorodeoxyglucose positron emission tomography showed a massive reduction of glucose metabolism in the basal ganglia and the frontal brain. The observed abnormalities possibly result from a disruption of frontostriatal circuits, presumably at the basal ganglia level. This case indicates that FD may cause exclusively behavioural alterations and that the associated hypometabolism in certain frontal areas is closely related to the clinical picture.