We report a 56-year-old man with so-called post-hemiplegic dystonia in the right lower extremity. His cranial CT scans and MRI revealed a small discrete lesion in the postero-lateral part of the contra-lateral putamen. The location of his putaminal lesion did not seem to correspond exactly to the leg area according to the topographical mapping of the monkey putamen. The mechanism of his focal dystonia is discussed including the possibility of the development of dopaminergic hyperactivity in the remaining area of the putamen as an account for his dystonic movement.