Abstract: A method for registering traffic data from mobile stations in a mobile telecommunication system. The mobile telecommunication system includes mobile switching centers and connected with these, base station controllers, so-called primary- and secondary base station controllers. Base stations are connected to the base station controllers, each base station covering a cell and each base station controller thereby covering a cell area containing several cells. Traffic data from a selected mobile is stored in the primary base station controller of the mobile. A trace invocation message is sent from the primary base station controller to the secondary base station controller, via the mobile switching center, when the mobile moves to a cell handled by the secondary base station controller. Registration of traffic data is thereafter effected in the secondary base station controller.