Abstract: A subsea Christmas tree coupling having a radially outer connection, for example a tree surface and a conductor housing, adapted to make a rigid joint with a conductor casing. A radially inner connection, for example a depending skirt of the subsea Christmas tree, is adapted to make a sealed joint directly with a casing hanger assembly of a mudline suspension system. The invention thus substantially eliminates the use of additional hangers besides those of the mudline suspension system, simplifying the coupling assembly, and providing the possibility of reduced stackup heights. The relatively compact and simple coupling results in shorter installation times and lower costs. The rigid joint between the coupling and the conductor casing ensures that any external loading is transferred to the conductor casing.