Aims: To describe a new, simple method of classiþcation for ossiþcations after total hip arthroplasty situated in the anterior, intertrochanteric area. (ÒAIOÒ). Methods: Axial (ÒLauensteinÒ) radiographs of 209 patients after THA using the transgluteal approach were retrospectively analysed regarding the occurrence AIO. These formations are situated in the anterior intertrochanteric region, therefore the major part of these ossiþcations cannot be identiþed by the well known and accepted methods of e.g. Brooker which rely on one anterior-posterior radiograph. By dividing the anterior intertrochanteric region in zones a simple method of classiþcation was developed. According to our method AIO can be classiþed by their appearance and their extent: Grade I describes bony islands without connection to the femoral bone, Grade II ossiþcations are clip or shield like formations without connection to the femoral bone, Grade III ossiþcations appear as solid exostoses in contact with the femoral bone. Results: 97 of 209 patients developed an AIO (48,4%), 12 ossiþcations were classiþed as Grade I (12,4%),3 ossiþcations were classiþed as grade II (3,1%), 82 out of 209 patients developed an AIO Grade III. 27 (13%) of the patients developed solid ossiþcations situated strictly in the anterior intertrochanteric region, thus solely veriþable by an axial radiograph. Conclusions: In our patient collective 13% developed a solid ossiþcation only veriþable by an axial radiograph due to a strictly anterior intertrochanteric location. By using the well accepted methods of classiþcation relying only on one single ap radiograph (Brooker, Arcq, deLee) these formations would not have showed up in our study. Our method of classiþcation is simple and can be easily combined with the classiþcations mentioned above.