We analysed clinical data in 80 genetically confirmed Huntington?s disease (HD) patients and measured the severity of the head of the caudate nucleus (HCN) atrophy using computed tomography-guided planimetry. The results were compared with measurements obtained in 43 age-matched healthy subjects. Mean planimetric measurements of the HCN differed significantly between the HD patients and healthy controls (p<0.001). We observed a significant inverse correlation between duration of HD and HCN planimetric values (p<0.001). Physiological atrophy of the HCN with age was also present in healthy controls, but did not overlap with values obtained in HD patients (p<0.01). Furthermore, we found in our patients a statistically significant inverse correlation between the number of CAG triplet repeats and the age at onset of HD (p<0.001). Neither the number of CAG triplet repeats, nor the age at onset of HD was found to be related to the character of the initial clinical symptoms (motor vs mental). Similarly, no relationship emerged between maternal or paternal inheritance and the number of CAG triplet repeats. Moreover, the type of inheritance did not influence the age at onset of HD in our patients. Planimetric measurement of the HCN appears to be a simple and useful paraclinical tool for the diagnosis of HD.