Ichthyomys stolzmanni is a supposedly rare ichthyomyine rodent known only from seven specimens from two localities, one in Ecuador and the other in Peru, which natural history is poorly known. We report four new records of the species from three localities in the department of Ayacucho, Peru. Current taxonomy recognizes the Ecuadorean population as I. s. orientalis Anthony 1923, and the Peruvian sample as I. s. stolzmanni Thomas 1893; but our morphological evaluation and descriptive statistics do not support the recognition of orientalis as a valid subspecies but rather as a synonym of stolzmanni. We also provide evidence that indicates this allegedly rare species is acquiring the status of nuisance species in man-made environment of the Peruvian puna. © 2010 Deutsche Gesellschaft für Säugetierkunde.