A 71 year-old hypertensive right-handed man presented a small intracerebral haematoma limited to the left subthalamic nucleus that resulted in right hemiballismus and a neurobehavioral disinhibition syndrome. The latter associated logorrhoea and euphoria, but there was no frontal signs nor mental confusion. The patient kept full insight into his mental change, that contrasted with his prior personality. Hemiballismus and the manic-like state resolved within 2 months. This case and some others from the literature illustrated that a focal lesion in the basal ganglia could result in manic-like affective change, and that a relation did exist between hyperkinetic syndrome and euphoria. Our case contrasted with most of the published cases of neurobevioral changes following basal ganglia discrete lesions, expressing as hypokinesia, apathy and loss of motivation. With reference to the functional circuits linking the frontal cortex and the basal ganglia, as described by Alexander, this syndrome of combined disinhibition of motricity, speech and affect could involve either the lateral orbito-frontal or the anterior cingulate loops, more especially the indirect pathways travelling through the subthalamic nucleus, lesion of which is known to disinhibit thalamo-cortical activity.