The montane pitviper is a small snake that can measure up to 85 cm long, but the average adult is 50 cm long. Males are longer than females.  Robust body with small, well differentiated head, and short tail, with post-ocular bands visible on both sides of the head. Characterized by a reticulated pattern, almost square-shaped on an ash-colored or brown base, although some individuals have an almost orange base color.

This species is active during the day and is terrestrial, with two defined activity patterns: morning and twilight. The montane pitviper is viviparous and relatively common. It has a very diverse diet that includes small mammals, birds, lizards, snakes, amphibians, and even arthropods.

It can be found from the southeast of Mexico to the west of Panama; in Costa Rica it is found in mountain forests in the Cordillera Central and the Cordillera de Talamanca, from 1460 to 2875 m of altitude.