Detachable needle protection cap for an injection device, comprising a housing, which can be detachably connected to the injection device at its distal end and, together with the injection device, defines a longitudinal axis and radial directions, at least two shell parts, which can be attached to an outer surface of the housing, a plurality of holding points in the form of a depression and a plurality of guide elements being arranged on the outer surface of the housing, the guide members being designed as elongate grooves or ribs and being approximately perpendicular to the longitudinal axis, at least one fastening element, a blocking element and at least one counter guide element being arranged on each of the inner sides of the at least two shell parts, characterized in that the shell parts can be attached to the housing by engagement of the fastening elements in the holding points of the housing, and release of the fastening elements of a shell part from the engagement with a holding point can be prevented by a blocking element of another shell part which is likewise attached to the housing, such that, when all of the at least two shell parts are fixed to the housing, non-destructive release of the shell parts is rendered impossible, and in that the guide counter elements are designed to be complementary to the guide elements as ribs or grooves, and the guide counter elements are inserted into the guide elements when the shell parts are attached to the housing, the grooves having undercuts and the ribs engaging into these undercuts during insertion, such that when the shells are attached to the housing, the shells are held in the radial direction relative to the housing. a housing, which can be detachably connected to the injection device at its distal end and, together with the injection device, defines a longitudinal axis and radial directions, at least two shell parts, which can be attached to an outer surface of the housing, a plurality of holding points in the form of a depression and a plurality of guide elements being arranged on the outer surface of the housing, the guide members being designed as elongate grooves or ribs and being approximately perpendicular to the longitudinal axis, at least one fastening element, a blocking element and at least one counter guide element being arranged on each of the inner sides of the at least two shell parts, characterized in that the shell parts can be attached to the housing by engagement of the fastening elements in the holding points of the housing, and release of the fastening elements of a shell part from the engagement with a holding point can be prevented by a blocking element of another shell part which is likewise attached to the housing, such that, when all of the at least two shell parts are fixed to the housing, non-destructive release of the shell parts is rendered impossible, and in that the guide counter elements are designed to be complementary to the guide elements as ribs or grooves, and the guide counter elements are inserted into the guide elements when the shell parts are attached to the housing, the grooves having undercuts and the ribs engaging into these undercuts during insertion, such that when the shells are attached to the housing, the shells are held in the radial direction relative to the housing.