A method and device are provided for determining a target altitude for an emergency descent of an aircraft that is to be reached by the end of the emergency descent. The method includes determining an initial target altitude representative of the initial position of the aircraft and then repeatedly determining a current target altitude along a reference horizontal distance. The current target altitude is compared to the initial target altitude and is used to update the emergency descent if the current target altitude is lower than the initial target altitude. Each target altitude is selected as the larger of a predetermined threshold altitude and a security altitude that ensures any obstructions along a remaining horizontal distance are avoided.