A 60-year-old female, who had been noted to have slowly progressive mental changes since the age of 40, subsequently developed irregular, abrupt, jerking movements of her limbs, and coordination and walking difficulty after 15 years. Her father, aunt and sister had also been suffering from similar involuntary movements and changes of personality. Neurological examination revealed slight dementia, choreic movements and the evidence of pyramidal tract signs; i.e., she showed general hyperreflexia of extremities, bilateral ankle clonus, and extensor plantar responses of lower extremities. laboratory data were all within normal ranges except iron deficiency anemia. Axial MRI showed moderate cortical atrophy, however, without dilatation of the frontal hours of lateral ventricles and the caudate head appeared normal. Our initial impression was dentatorubropallidoluysian atrophy (DRPLA). However, the genetic analysis of her peripheral leukocytes disclosed an expansion of the CAG repeats (43 copies) in the IT15 gene in chromosome 4p, indicating the diagnosis of Huntington's disease (HD). CAG repeats in chromosome 12, known to link with DRPLA, was not expanded. Thus, this case is unique in that the classical symptomatologies of HD was betrayed by the presence of prominent pyramidal tract signs. This patient may be of importance in demonstrating the diversity of neurological symptoms and neuropathologies caused by CAG trinucleotide repeats in HD.