Lewis Glacier on Mt Kenya has a unique history of detailed study, making it among the best documented tropical glaciers. Here we present (i) a new ice volume determination based on a bedrock DEM constructed from GPR data acquisition and (ii) the glacier's mean mass balance rates over the last 76 years derived from volume and area estimates based on seven historical maps and the newly determined bedrock topography. Total ice volume in 2010 was 1.90 ± 0.30 × 106 m3 with a mean (maximum) ice depth of 18 ± 3 m (45 ± 3 m), which is one order of magnitude larger than previously published values. In 2010, the glacier had lost 90% (79%) of its 1934 glacier volume (area), with the highest rates of ice volume loss occurring around the turn of the century. Computed mean mass balance rates, covering the whole period of glaciological surveys of Lewis Glacier, provide the longest record of tropical glacier change and show that the mean mass balance rate varies consistently with global estimates, but the magnitude is always more negative than in other regions.