The morphology of pallidal neurons was analyzed quantitatively in Golgi-impregnated brains of men and macaques (Macaca irus). Selected neurons were drawn with a camera lucida and reconstructed from serial sections. Dendritic arborizations were analyzed in three dimensions using a video computer microscope (Yelnik et al., '81). Morphological (topological and metrical) parameters were computed, and the overall geometry of arborizations was studied in three dimensions with the aid of principal component analysis (Yelnik et al., '83). Statistical tests were used in order to compare human with simian large neurons and the lateral with the medial pallidum. All neurons were found to belong to a single neuronal population. Particular neurites may be added randomly onto pallidal dendrites, mainly in the lateral pallidum. Large pallidal neurons are characterized by sparsely branched dendritic arborizations (4 stems, 13 tips) with thick, smooth, and long dendrites (longest dendrite = 1,000 micron, total dendritic length = 7,600 micron). All arborizations are discoidal in shape with mean dimensions of 1,500 X 1,000 X 250 micron. Pallidal discs are always parallel to the lateral border of each pallidal nucleus and thus perpendicular to striatal axons to which they present their greatest extent. They may be traversed by a large number of these axons. The existence of other pallidal neuronal groups, "intermediate" and "local circuit" neurons, identified in their fine morphological features by François et al. ('84), was confirmed quantitatively in the present study.