Species of AtractieJlales (Auriculariaceae s.I.), Exidaceae, Sirobasidaceae and TremeJlaceae are reported as new for Costa Rica or as new to science, Tremella coalescens L.S. Olive, Sirobasidium minutum Kisim.,Oberw. & Gómez sp. nov., Heterochaete vitrea Kisim., Oberw. & Gómez sp. nov ., Exidiopsis mucedinea (Pat.) KWells, Helicogloea aurea Baker, Saccoblastia sphaerospora Mtlller and .occultifur internus (L.S. Olive) Oberw. All the new species are described and illustrated. Since the original material coJlected in BraziJ by MtlJler is lost, a neotype for Saccoblastia sphaerospora MtlJler is proposed. This Costa Rican collection represents the first record since the discovery of the species in 1891. Hyphoderma argillaceum (Bres.) Donk is reported for the first time from Costa Rica as the fungal host of Occultifur internus.