The invention relates to a method and a device for determining the compatibility between an adapter, which is to be inserted into a third-party joint ball type to be replaced, and an outer cone (10) of a prosthesis shaft of a modular joint prosthesis, which is inserted in the femur during revision surgery. The aim of the invention is to provide a method and a device for determining the compatibility of an adapter of a joint prosthesis, which allow to combine modular components of a joint prosthesis from different manufacturers, to simplify revision surgery and to insert joint balls made of ceramics or metal into an already lying shaft in a precise fit. This aim is solved by a method in which a test body (1) of a set of test bodies having various inner cones, comprising a marker (7) and a length measuring scale (8), is fitted onto the outer cone of the shaft of the joint prosthesis and, subsequently, the adapter fitting on the outer cone of the joint prosthesis is determined by successively testing the inner cones for compliance with an admissible minimum distance between the front faces of the outer cone of the shaft of the joint prosthesis and the inner cone and for compliance with an admissible predefined insertion depth of the outer cone of the shaft of the joint prosthesis in the inner cone of the test body.
