The present invention discloses a method, a system and a computer program for the effective evacuation of a building in an emergency, in which at least one elevator can be used as an evacuation aid. In the method the group control of the elevators monitors the numbers of people on the different floors of the building. The floor on which it is assumed are most people is set at each moment of monitoring for a greater priority in an evacuation situation. Taking into account the limited supply power a free elevator car is directed to the floor of the greatest priority, at which the elevator is filled. The full elevator is directed without stopping to the exit floor of the building. The system monitors by means of detectors the safety of the different parts of the building and directs people if necessary to a safe evacuation location to wait for an elevator. A so-called Traffic Forecaster can be used as an aid in defining the priorities.