Three species of aquatic frogs of the genus Telmatobius (T. ceiorum, T. laticeps and T. pisanoi) were historically present in montane streams of Tucumán Province (Argentina). We conducted exhaustive surveys between 2001 and 2005 in three types of environments: (1) streams in mountain forests (Yungas) from 1300 to 1900 m above sea level, (2) streams in montane grasslands 2000 to 4000 m, and (3) streams in Prepuna shrublands from 2000 to 3500 m. Small numbers of T. pisanoi were found at the edge of its original distribution area, but were absent from the sites where the species was originally abundant. The other two species were absent from the surveyed streams, including historic localities, and are presumably extinct. Several factors are suggested as possible causes of this decline, including (a) an unusual dry and warm period that preceded the last record for T. laticeps and T. pisanoi, (b) the presence of exotic salmonids in the forest streams where T. ceiorum historically lived, (c) the expansion of the trout stockings in the historical distribution area of T. laticeps, (d) an increase in erosive processes and debris flowing events in montane streams, and (e) the presence of chytrid fungus.