A method for controlling the roaming of a mobile unit in mobile networks

The invention refers to a method for controlling the roaming of a mobile unit (1) in mobile networks. The mobile unit (1) is associated with a home network (HN) and sends a registration request (UL) for registering in the home network (HN) via a visited network (VN). A control unit (2,3) performs the following steps. If it is observed (S101) that the mobile unit (1) has sent a preceding registration request for said visited network (VN) or said roaming region (VN, VN') before the detected registration request (UL) and observed (S102) that the visited network (VN) is not a preferred network, disapproving (S46) the registration request (UL). If it is observed (S101) that the mobile unit (1) has not sent a preceding registration request for said visited network (VN) or said roaming region (VN, VN') before the detected registration request (UL) and regardless of whether the visited network (VN) is a preferred network, approving (S43) the registration request (UL) for the home network (HN), resulting in a registration of the mobile unit (1) in the home network (HN). Thereafter a list of preferred networks (RL) is sent to the mobile unit (1) for choosing a preferred network from the list (RL) as a visited network (VN) during the next attempt to register in the home network (HN).