A method and device for ensuring the safety of a low-altitude flight of an aircraft is disclosed, wherein low-altitude flight is flight along a flight trajectory at low altitude, for example 500 feet, that allows an aircraft to follow as closely as possible the terrain being over-flown. To avoid collision with the terrain, a safety corridor, devoid of any obstacle, is determined which is delimited on either side of the lateral trajectory, and whose width depends on a global uncertainty, and the aircraft is guided along the flight trajectory, avoiding any exit of the aircraft from the safety corridor.