The topographical distribution of density and the soma size of retinal ganglion cells (RGCs) were studied in the St. Kitts green monkey (Cercopithecus aethiops sabeus). The total number of RGCs, estimated from light microscopic analysis of wholemounted and of transversely sectioned retinae, ranged between 1,183,721 and 1,273,715 (mean 1,228,646). These estimates are comparable to the number of optic nerve fibres (1,220,000) estimated from semithin sections. The topographic distribution of RGCs shows a strong centroperipheral gradient. The soma size distribution of RGCs in Nissl-stained flatmounts falls within a range of between 5.7 microm and 22.9 microm and is comparable to other primate species. Somata of RGCs were found to be generally smaller within the fovea than in peripheral regions. Ganglion cells, as reported for other diurnal primates, are nonuniformly distributed with a slight nasotemporal elongation of isodensity contours, and they exhibit nasotemporal asymmetry in the frequency distribution of soma size. The topography of the RGC distribution of this semiarboreal, ground-dwelling monkey is similar to what has been found in other diurnal Old World species.