Selection for biparental care is considered to be an important factor favoring the evolution of monogamy if the value of exclusive cooperation in care for mutual offspring outweighs the benefits of polygamy for either sex. Support for this hypothesis has come primarily through parent removal experiments in avian taxa. We tested this hypothesis in the first known example of a socially and genetically monogamous amphibian, the mimic poison frog (Ranitomeya imitator). Biparental care in R. imitator is characterized by egg attendance, tadpole transport, and feeding of tadpoles with unfertilized trophic eggs. Using a male removal experiment, we found lower tadpole growth and lower survival for widowed females compared with control families. We demonstrate that in addition to egg attendance and tadpole transport, male parental care is critical for offspring survival throughout larval development. Previous research has shown the importance of female trophic egg provisioning of tadpoles in R. imitator. This, coupled with the results of the present study demonstrating the adaptive value of male care, supports the hypothesis that selection for biparental care has driven the evolution of monogamy in an amphibian. © The Author 2013. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.