There is provided mechanisms for adaptive user-specific beam forming. A method is performed by a network node. The method comprises acquiring uplink user-specific spatial channel characteristics for a wireless device. The method comprises acquiring a set of downlink port mappings for the wireless device. The method comprises adaptively configuring user-specific ports for the wireless device by using the uplink user-specific spatial channel statistics to determine a downlink user-specific port mapping from the set of downlink port mappings, thereby providing user-specific beam forming for the wireless device.