First record of the subfamily Pycnocheiridiinae from South America, with the description of Leptocheiridium pfeiferae gen. n., sp. n. (Arachnida: Pseudoscorpiones: Cheiridiidae). -The cheiridiid subfamily Pycnocheiridiinae is recorded for the first time from south America, Leptocheiridium gen. n. and its type species pfeiferae sp. n. are described and illustrated. The new genus shares with Pycnocheiridium Beier, 1964 (type genus of the Pycnocheiridiinae Beier, 1964) the same morphology of walking legs, eight trichobothria on the fixed chelal finger, only two on the movable finger, and the presence of strongly clavate vestitural setae. Leptocheiridium gen. n. is well characterized by the shape of its slender pedipalps, the presence of three sub-equal setae in the rallum, the presence of five setae on the cheliceral hand, the morphology of the female galea, and the presence of a well-developed transverse furrow on the carapace.