Mass balance and climate sensitivity of Glaciar Perito Moreno (GPM), one of the main outlet glaciers of Hielo Patagónico Sur (southern Patagonia icefield), were investigated. Field measurements were carried out from 1995 to 2003, including ice ablation and velocity at stakes, seismic profiling, bathymetry of the lake near the calving fronts and meteorological data. The database was complemented by satellite observations, to derive the motion field by interferometric data, map glacier boundaries and snowlines from multi-year time series of radar images, and obtain glacier topography from the Shuttle Radar Topography Mission. In September 2003, GPM started to dam the southern arm of Lago Argentino, resulting in a maximum rise of the lake level of 9.35 m before the dam burst in March 2004. The ice dam formed again in August 2005, bursting in March 2006. Analysis of mass fluxes indicates no long-term trend in mass balance. This behaviour, contrasting with most retreating glaciers in the vicinity, can be attributed to a particular glacier geometry. Monthly climate sensitivity characteristics for glacier mass balance were derived using a degree-day model, showing similar importance of both temperature and precipitation. Also, the reconstruction of the mass balance for the last 50 years from local climate data shows a near-steady-state condition for GPM, with some small fluctuations, such as a slightly positive balance after 1998, that may have triggered the minor advance leading to damming events in 2003 and 2005.