Helminthosphaeria, a genus of pyrenomycetes, is monographed. Its members occur on basidiomata of species of the Aphyllophorales. The following species are included: H. clavariarum, the type, H. odontiae, H. corticiorum, and the new species H. hyphodermiae. A new family, Helminthosphaeriaceae, is proposed for the genus. Litschaueria is found to be a synonym of Helminthosphaeria.