Cranial suture closure is examined in two species of South American monkeys, Saimiri sciureus and Saguinus nigricollis. Sequences in closure were sought as indicators of skeletal age. Some sutures seem to be more reliable determinants of skeletal age than others, and these sutures and their sequence of closure are different in the two species examined. The sphenooccipital synchondrosis and the palatal portion of the Interpremaxillary suture show regular fusion associated with age in both species. In Saimiri the maxillopremaxillary sutures are also reliable indicators of age, whereas they are not in Saguinus; however, in the latter the presphenoid‐postsphenoid synchondrosis closes regularly whereas it does not in Saimiri. In Saimiri the predictable sequence is (1) maxillo‐premaxillary, (2) transverse maxillo‐premaxillary, (3) spheno‐occipital, (4) interpremaxillary. In Saguinus it is (1) presphenoid‐postsphenoid, (2) spheno‐occipital, (3) interpremaxillary. It is possible that the sequences of suture closure and the variability in this process may indicate genetic and taxonomic relationships.