Nematoctonus (Hyphomycetes) and Hohenbuehelia (Agaricales, Pleurotaceae) are the names for the asexual and sexual stages of a genus of nematode-destroying fungi (Basidiomycota). Six morphospecies of Nematoctonus, all previously described, were isolated from fruiting bodies of Hohenbuehelia and from 439 samples of soil and organic debris collected in all 12 Holdridge life zones in Costa Rica. Nematoctonus was recorded in all but three life zones at the lowest and highest altitudes: tropical dry forest, tropical moist forest, and subalpine rain paramó. Isolates of Nematoctonus were identified by the micromorphology of their conidia and adhesive knobs, which are usually an hourglass-shaped secretory cell surrounded by a drop of mucilage. Adhesive knobs were found either exclusively on hyphae in predatory species ( Nematoctonus robustus F.R. Jones), exclusively on germinated conidia in parasitoid species ( Nematoctonus leptosporus Drechsler, Nematoctonus pachysporus Drechsler, and Nematoctonus tylosporus Drechsler) or on both hyphae and germinated conidia in a group we term “intermediate predators” ( Nematoctonus angustatus Thorn & G.L. Barron, Nematoctonus geogenius Thorn & G.L. Barron, and one monokaryotic isolate of N. robustus). Teleomorph–anamorph connections, made by culturing the anamorph from a teleomorph fruiting body, were made for N. angustatus (Hohenbuehelia angustata (Berk.) Singer), N. geogenius (Hohenbuehelia petalodes (Fr.) Schulz.), N. leptosporus (an unidentified Hohenbuehelia), and N. robustus ( Hohenbuehelia grisea (Peck) Singer).