CT has been performed in five patients affected by amyotrophic choreo-acanthocytosis (ACA) and bicaudate diameter, bicaudate index and frontal horn/bicaudate ratio (FH/CC) have been evaluated. Findings have been confirmatory of caudate nuclei atrophy as shown by previous ACA autopsy reports, but did not differ from Huntington's chorea CT picture. There was no correlation between CT measurements and age, illness duration or degree of hyperkinesia in contradistinction to that reported for Huntington's chorea.