Nine physically healthy, adult autistic men, with normal or near normal intelligence, and 13 healthy male controls were examined in a CT brain scan study. CT scans were analysed with a fully automated computer-assisted program, and regional brain radiodensities were measured with careful attention to artefacts. Autistic patients revealed significantly larger third, but not lateral, ventricular size and significantly lower mean caudate, but equivalent mean frontal and thalamic, radiodensities compared to controls. The sizes of the Sylvian fissures and interhemispheric fissure were equivalent between groups. The findings are consistent with selective subcortical abnormalities in autism.