Brain structure volume, total number of neurons and neuronal density. Range of the volume of examined regions from the largest (thalamus, putamen, and caudate) to the smallest (inferior olive). The volume of all four striatum subdivisions, including putamen, caudate nucleus, globus pallidus, and nucleus accumbens, is greater in subjects with autism, but the difference in this volume between affected and control subjects is significant only in the caudate and nucleus accumbens (black stars). The total number of neurons was found to be significantly less only in the second layer of the entorhinal cortex (white star) when covariates were not entered in the analysis. Although the total number of neurons does not reveal significant differences, the numerical density is significantly reduced in the nucleus accumbens and putamen of subjects with autism. The significantly lower numerical density of neurons is observed in the lateral nucleus of the amygdala (white star), but not in other amygdala nuclei. Cerebellar volume and the volume of the molecular and granule cell layers, cerebellar white matter, and cerebellar nuclei do not reveal differences between affected and control subjects; however, the total number of Purkinje cells was 25% less (p< 0.03) in the group with autism (12.1 million) than in the control group (16.0 million). The numerical density of Purkinje cells was also significantly less (p < 0.004) in the affected group than in the control group (488/mm3 and 645/mm3, respectively). Th, Thalamus; Pu, putamen; CN, caudate nucleus; AH, Ammons horn; EC, entorhinal cortex; GP, globus pallidus, Cl, claustrum; Am, amygdala; DN, dentate nucleus; Ac, nucleus accumbens; SN, substantia nigra; MBC, magnocellular basal complex; LGB, lateral geniculate body; IO, inferior olive; Crb, cerebellum; ML, molecular layer; GCL, granule cell layer; WM, white matter; Nu, cerebellar nuclei.