To determine if memantine in doses of 10 mg BID affects memory, cognition, and behavior in patients with Huntington's disease (HD).

Results of several published clinical trials suggest that memantine has a beneficial effect in dementing conditions, such as Alzheimer's disease; however, the effects of memantine on cognitive and behavioral function in HD are unknown. Our hypotheses are that HD patients who are administered memantine will show improved performance on psychometric tests of memory and executive functions in addition to behavior and that patients treated with memantine will show more improvement after six months than after three months of treatment.

Inclusion Criteria:

• Men or women aged 18 or older.
• Diagnosis of HD with current complaints of memory or concentration difficulties.
• Dementia Rating Scale score of <129, to ensure that patients have sufficient cognitive impairment.
• Adequate visual and auditory acuity to allow neuropsychological testing.
• Good general health with no additional diseases expected to interfere with the study.
• Patient is not institutionalized.
• Sufficient English skills to complete all testing without assistance of an English language interpreter.
• Availability of a responsible caregiver who agrees to supervise administration of study drug, monitor the patient's compliance and adverse events, and accompany the patient to all clinic visits.

Exclusion Criteria:

• 1. Any significant neurologic disease other than HD.
• Severe psychotic features or other severe psychiatric problems within the last three months which could lead to difficulty complying with the protocol.
• History of alcohol or substance abuse within the past two years (DSM IV criteria).
• Any significant systemic illness or unstable medical condition which could lead to difficulty complying with the protocol.
• History of MI in the past year or head trauma with loss of consciousness greater than 20 minutes.
• Insulin-requiring diabetes.
• Use of any FDA approved cognitive enhancing prescription medications or investigational drugs within 30 days.
• Use of ginkgo biloba or DHEA within four weeks prior to baseline.
• Use of narcotic analgesics within 4 weeks prior to baseline.
• Patients who, in the investigator's opinion, would not comply with study procedures.