New World primates comprise a diverse group of neotropical mammals that suddenly appeared in the Late Oligocene deposits of South America at around 26 million years ago (MYA). Platyrrhines seem to have separated from Old World anthropoids ca. 35 MYA, and their subsequent diversfication is not well documented in the fossil record. Therefore, molecular clock studies were conducted to unveil the temporal scenario for the evolution of the group. In this study, divergence times of all splits within platyrrhines until the generic level were investigated, using two different gene data sets under relaxed molecular clocks. Special attention was paid to the basal diversification of living platyrrhines and to the basal split of the modern Cebidae family, since these nodes were reported to be phylogenetically difficult to resolve. The results showed that analyses from various genomic regions are similar to estimates obtained by early single-gene studies. Living New World primates are descendants of ancestors that lived in the Early Miocene, at around 20 MYA, and modern Cebidae and Pitheciidae appeared ca. 16.9 and 15.6 MYA, respectively. The last common ancestor of living Atelidae is 12.4 million years old, making this clade the youngest New World primate family; at approximately the same time, modern Callitrichinae was evolving (11.8 MYA). The gap between the Platyrrhini/Catarrhini separation and the last common ancestor of living Platyrrhini may be as big as 20 million years. Paleontological and geoclimatological evidence corroborates that the sudden appearance of modern families may be a consequence of environmental changes during the Miocene. Am J Phys Anthropol, 2007 © 2006 Wiley-Liss, Inc.