Despite evidence for spinal cord involvement, it remains unclear whether spinal cord atrophy exists in early Huntington's disease. We studied magnetic resonance images, covering both brain and upper cervical cord, in two cohorts of Huntington's patients and in one cohort of Alzheimer's patients. All cohorts included healthy controls comparable with regard to age and gender. We found significant spinal cord atrophy in both cohorts of Huntington's patients but not in the cohort of Alzheimer's patients. Furthermore, spinal cord atrophy correlated with motor symptoms indicating that spinal cord atrophy occurs in the clinical stages and does not result from abnormal development.