The Deterministic Distributed Hydrological System (Yu. B. Vinogradov, State Hydrological Institute, Saint-Petersburg, Russia) was applied to perform numerous simulations implemented across Eastern Siberia within the Lena river basins to evaluate the model's representation of the hydrological cycle for mountainous conditions. Special aspects of runoff processes modeling in mountainous areas accounting for slope inclination and exposure, snow drifting, glaciers impact, meteorological input interpolation and their application in the used model are discussed. The results of runoff simulation for six mountainous watersheds of different size in conditions of considerable uncertainties and their statistical evaluation are presented.