The Amazon marmosets are poorly known and severely threatened – endemic to the arc of deforestation in southern Amazonia. Based on data from field expeditions across this global deforestation frontier, we provide new records and extend the range of Mico chrysoleucos, provide new records and refine the range of M. acariensis, report the first records of a species of Mico on permanently flooded forests, and hypothesize the existence of a hybrid zone of these two species and also M. melanurus.