Mounting device for mounting or demounting a wind turbine blade (14) to or from a hub which is located on a nacelle at the top of a wind turbine tower (12). The mounting device comprises a sledge which comprises a support structure and a gripping structure. The support structure is adapted to releasably grip the wind turbine tower and adapted to guide the sledge along an outer surface of the wind turbine tower between a bottom end position and a top end position of the tower. The gripping structure is adapted to provide a releasable fixation of the wind turbine blade in a fixed orientation relative to the gripping structure. The sledge is adapted to be moved along the tower by a combination of the support structure and a cable connection to the top end. A tilt device (17) is arranged between the support structure and the gripping structure to facilitate tilting of the gripping structure relative to the support structure.