The invention relates to an endoprosthesis, particularly for the at least partial replacement of a long bone, comprising a plug-in connection for connecting a shaft (2) to another part (1) of the prosthesis, wherein the plug-in connection (3) comprises an axial projection (33) and a socket (34). According to the invention, provision is made that a radial transverse channel (53) is provided on one part of the plug-in connection (3), said radial transverse channel (53) engaging behind the plug-in connection and having a center axis (55) that is offset (d) relative to the axis (56) of a transverse bore (52) arranged on the other part of the plug-in connection, and a clamping element (6) which is to be inserted into the transverse channel (53) and whose point (62), in the inserted state, engages in the transverse bore (52). In this way, it is possible to achieve an effective securing action even in the event of an unfavorable tolerance pairing, without adversely affecting the sensitive projection itself.