Spontaneous object grouping by two capuchin monkeys (Cebus apella) ranging from 1 to 4 years of age was investigated. Subjects' spontaneous interactions with groups of objects were recorded. Similarly to human infants and chimpanzees, capuchins increased with age the size of groups, the rate of vertical constructions, and of contemporaneous groups, i.e., of groups made simultaneously or close to another. However, capuchins lagged behind human infants and, partly, to chimpanzees in that they failed to develop alignments of objects, or spatial correspondences between contemporaneous groups. Capuchins' constructive processes were similar to those of chimpanzees and different from those of human infants. Nonhuman primates increasingly manipulate objects together with the same part of their body. In these instances, no specific spatial relations among objects as detached units are detectable. In fact, objects are related to one another only incidentally to the simultaneous relations of each object to the self. Therefore, nonhuman primates increasingly manipulate objects in relation to their body.