A method for determining location of a failure causing degradation of a service in a mobile communications network is disclosed. Service trajectories for the mobile terminals are determined (104) by correlating earlier obtained movement trajectories (102) of individual mobile terminals with service session records of the mobile terminals. In the next step distributions of the service trajectories of mobile terminals with degraded service are determined and then a network element around which the service trajectories converge is identified (108) as the location of the failure. An apparatus, a communications network and a computer program product are also disclosed.