The surface movement of Daugaard-Jensen Gletscher, East Greenland, a fast-moving outlet glacier from the Greenland ice sheet, was determined by means of theodolite measurements, using intersections from observation stations on bedrock, once or twice a day, during a ten-day period. With a gap of about three weeks, the observation programme was resumed for another three days which allowed “long term” mean velocities to be calculated, as references for a study of velocity fluctuations on time scales in the range 2–10 days. Various methods of analysing non-synchronous theodolite measurements on fast-moving glaciers are discussed, and previously-reported large velocity fluctuations are critically reviewed. It is concluded that, on the time scales studied, velocities in the frontal region of Daugaard-Jensen Gletscher fluctuate by up to 15%. However, on one occasion, a velocity increase of more than 50% was observed, lasting for about 7.5 hours. This event is inferred to be the result of a sudden increase in the water pressure of the subglacial drainage system, caused by the tapping of an ice-dammed lake behind the glacier front. The more moderate velocity fluctuations are most likely also due to changes of the subglacial hydraulic system.