PURPOSE OF THE STUDY: The aim of the study was to compare the exactness of correction of proximal femoral deformities between the patients treated with AO angled blade plates and those managed by the cannulated paediatric osteotomy system (CAPOS). MATERIAL AND METHODS: In the period from 1994 to 2003, corrective osteotomy of the proximal femur using the conventional AO angled blade plate (90°, 120°, 130°) was performed on 57 hips in 42 children. In the period 2004-2012, 68 hips in 59 children were treated by the CAPOS method. In each child, the pre- and post-operative X-ray views were compared and a real deviation from the pre-operative plan was determined. A deviation larger than 10° in the frontal plane was recorded as an error. Penetration of the blade into either the posterior or the anterior femoral neck cortex seen on axial views was regarded as an error as well. RESULTS: Corrective osteotomy with AO angled blade plates performed on 57 hips failed in 12 (21.1%) on anteroposterior views and six hips (10.5%) on axial views. Of 68 hips treated by the CAPOS, failure was recorded in four (5.9%) and one (1.5%) on anteroposterior and axial views, respectively. DISCUSSION No information on the CAPOS technique is available in either international or national literature, with the exception of our preliminary report. On the other hand, locking compression plates for paediatric hips, developed later, have been described in several publications. The authors appreciate a higher accuracy of bone correction and higher stability for the whole fixation, which results in earlier mobilisation of the treated extremity. These advantages are also true for CAPOS instrumentation. CONCLUSIONS: The CAPOS can be seen as an intermediate stage of development between conventional angled blade plates and locking compression plates for paediatric hips. However, it should be noted that surgery involving insertion of an angled blade plate takes less time than insertion of a locking compression plate. For this reason, in procedures combining femoral osteotomy with, for instance, triple pelvic osteotomy the use of CAPOS instrumentation is still preferred.