Huntington's disease is a progressive neurodegenerative disease in which the molecular abnormality has recently been described. Before the availability of this molecular marker diagnosis depended on clinical findings, supported in some instances by neuroimaging using CT or MRI. The imaging modalities may show atrophy of the heads of caudate nuclei in affected people. An attempt was made to validate these imaging findings using the molecular test as "gold standard." Retrospective analysis of cranial CT in 16 patients with Huntington's disease and 16 age and sex matched controls was performed. There was a highly significant difference in caudate head size (P < 0.00001) between patients with Huntington's disease and control subjects. However, the sensitivity of diagnosis based on radiological examination alone was only 87.5% in this study. Thus the sensitivity of CT is insufficient to justify its routine use in the investigation of suspected Huntington's disease, unless genetic tests are negative and other diagnoses need to be excluded.