The aim of this study is to evaluate the role of endoscopy as diagnostic and prognostic method for Ficat and Steinberg stage IIIA and IIIB lesions by assessing the efficacy, risks and complications of this method. In a prospective study from January 2008 until September 2013, nine patients (13 hips) were assessed. In nine hips the disease was stage II, in three hips stage III and in one hip stage IV. Evaluation included x-rays, magnetic resonance and bone scintigraphy. After femoral head decompression, the borders of the removed necrotic area were investigated under direct visualisation by means of endoscopy in order to assess the vitality status of the surrounding bone. Endoscopic evaluation was successful in nine hips. The visualisation of healthy bone borders after removing the necrotic bone was not possible in four cases. The preoperative MRI findings were in correlation to our endoscopic findings in five out of nine cases. There were no cases of cartilage perforation, femoral neck fracture and other intra and postoperative complications. Endoscopic evaluation of the removed necrotic bone can greatly improve the therapeutic effect by visualising the borders of the decompressed bone area and provide information regarding the necessity for bone graft and the type of graft required.