In order to determine a spectral route for a given connection in an optical telecommunications network (T) between a starting node (ON1) and a destination node (ON6) of the network, the method consists in: using a conventional routing method to determine one or more candidate spatial routes (Route i, Route 2) connecting the starting node (ON1) to the destination node (ON6), each candidate spatial route comprising a sequence of route segments, each segment connecting two nodes of the network directly and being adapted to support a plurality of spectral routes.