It has a single tubular, dark green leaf and up to fifteen greenish or light brown flowers with a white labellum.

Prasophyllum perangustum is a terrestrial, perennial, deciduous, herb with an underground tuber and a single tube-shaped, dark green leaf which is 180–250 mm (7–10 in) long and 2–3 mm (0.08–0.1 in) wide near its reddish base.

The edges of the upturned part of the labellum are slightly wavy and there is a thickened, fleshy green, channelled callus in its centre.

[2][3][4] Prasophyllum perangustum was first formally described in 1998 by David Jones from a specimen collected near Knocklofty and the description was published in Australian Orchid Research.

The main threats to the population are weed invasion, inappropriate fire regimes and track maintenance.