The present invention discloses a method for optimal routing of the elevators in an elevator system in a situation where the supply power received by the system is limited e.g. due to emergency power operation. In the invention, routes are optimized by using a cost function to which has been added a term containing the summed instantaneous power consumed. Power consumption is monitored in real time, and the elevators need a start permission from the control system. A route alternative that exceeds the power limit is penalized in the cost function by a so-called penal term. With the elevator routing obtained as a result, the instantaneous power consumed by the system remains continuously below the set power limit. Some call can thus be postponed to be served later. By the method of the invention, the number of elevators serving passengers in an emergency power situation can be varied dynamically.