Synosis Townes is a widely distributed genus of the family Ichneumonidae; most species recorded occur in the Old World and only two were formerly known to occur in the New World. Herein we describe Synosis rubinus sp. nov., Synosis cosnipatensis sp. nov., Synosis gauldi sp. nov. and Synosis townesi sp. nov. collected in various Peruvian cloud forests. A generic diagnosis and a key to the species occurring in the New World is also presented. http://www.zoobank.org/urn:lsid:zoobank.org:pub:8E5FA67F-F80A-4D78-8E5E-7CC8D6662396.