A method for mounting rotor blades of a wind turbine , wherein the wind turbine has a rotor hub with three rotor blade ports (111-113), on which a respective rotor blade is to be mounted, with the following steps: turning the rotor hub until the first rotor blade port is in a 90° or in a 270° position, fastening a first end of a first section of a mounting arm to the first rotor blade port , wherein the mounting arm has the first section and a second section , which are coupled with each other via a hinge , so that the angle between the first and second sections can be varied, turning the rotor hub with the help of the mounting arm , until the second rotor blade port is in a 270° or in a 90° position, wherein the angle between the first and second sections of the mounting arm is varied while turning the rotor hub , horizontally lifting a first rotor blade , in particular by means of a rotor blade traverse and a crane rope , so that the first rotor blade is horizontally mounted to the second rotor blade port of the rotor hub , turning the rotor hub with the help of the mounting arm , until the third rotor blade port is in a 270° or in a 90° position, mounting the second rotor blade to the third rotor blade port , in particular with the help of a rotor blade traverse and the crane rope , turning the rotor hub with the help of the mounting arm , until the first rotor blade port is in the 90° or in the 270° position, demounting the mounting arm from the first rotor blade port , mounting a third rotor blade to the first rotor blade port , in particular with the help of the rotor blade traverse and the crane rope , wherein the angle between the first and second sections of the mounting arm is varied by the swivel hinge . turning the rotor hub until the first rotor blade port is in a 90° or in a 270° position, fastening a first end of a first section of a mounting arm to the first rotor blade port , wherein the mounting arm has the first section and a second section , which are coupled with each other via a hinge , so that the angle between the first and second sections can be varied, turning the rotor hub with the help of the mounting arm , until the second rotor blade port is in a 270° or in a 90° position, wherein the angle between the first and second sections of the mounting arm is varied while turning the rotor hub , horizontally lifting a first rotor blade , in particular by means of a rotor blade traverse and a crane rope , so that the first rotor blade is horizontally mounted to the second rotor blade port of the rotor hub , turning the rotor hub with the help of the mounting arm , until the third rotor blade port is in a 270° or in a 90° position, mounting the second rotor blade to the third rotor blade port , in particular with the help of a rotor blade traverse and the crane rope , turning the rotor hub with the help of the mounting arm , until the first rotor blade port is in the 90° or in the 270° position, demounting the mounting arm from the first rotor blade port , mounting a third rotor blade to the first rotor blade port , in particular with the help of the rotor blade traverse and the crane rope , wherein the angle between the first and second sections of the mounting arm is varied by the swivel hinge . <EOS>