We estimated the total neurone number, glial number, and glial index (ratio glial cells/neurone) in the thalamic mediodorsal nucleus (MD) in seven patients suffering from Huntington’s disease (HD; four males, three females, mean age 52.4 ± 13.6 years) and age- and sex-matched controls (four males, three females, mean age 53.6 ± 12.1 years) by means of a stereological protocol. The mean total neurone number (N_T¯) in the MD of controls was 2,985,188 ± 174,710, the mean glial number (G_T¯; astrocytes, oligodendrocytes) 21,785,008 ± 2,986,678, and the glial index 7.29 ± 0.88. In HD, the average neurone number was decreased by 23.8% to 2,275,321 ± 247,162 (Mann-Whitney U-test P < 0.05), the mean glial number by 29.7 % to 15,318,895 ± 1,722,524 (Mann-Whitney U-test P < 0.05), the glial index was slightly reduced to 6.81 ± 1.06. Gallyas’ impregnation for the demonstration of fibrous astroglia gave strongly positive results in all cases with HD and negative results in the controls. The morpho-functional correlation of the results is complicated because individual variability, presence of segregated and parallel neuronal circuits, and plasticity of the adult human CNS must be considered.