We present climate data, direct surface mass balance (SMB) observations and model results for Mocho Glacier in the Chilean Lake District. Mean annual temperature on a nunatak of Mocho Glacier at an elevation of similar to 2000 m was +2.6 degrees C in 2006-15 and mean annual precipitation in Puerto Fuy (13 km from the glacier, at an elevation of 600 m) was 4000 mm for the same period. High interannual variations in the SMB of Mocho Glacier were observed. A simple SMB model is able to reproduce the observed annual variations in SMB, but fails to predict the steep observed mass-balance gradient. The average of the measured annual glacier mass balances in the four hydrological years 2009/10-2012/13 was -0.90 m w.e. a(-1) and the average modelled annual glacier mass balance 2006/07-2014/15 was - 1.05 m w.e. a(-1). The observed distributed ablation shows a clear altitudinal dependency, while accumulation is determined by patterns of snow drift as well. These patterns are only poorly represented in the model and have to be included in order to be able to reproduce a realistic SMB map of the glacier.