Background: Herniated lumbar disc segment site is not noly the important factor for selecting the surgical approach for percutaneous endoscopic lumbar discectomy, but also a key factor in determining the difficulty of operation.The currently known classifications are all two-dimensional space genotyping, its can not show the full three-dimensional informations of the herniated lumbar disc.Therefore, it is necessary to develop a new classification to fully reflect the three-dimensional informations of the herniated lumbar disc which can be used for guiding the surgical approach selection of percutaneous endoscopic lumbar discectomy, judging the difficulty of the surgery, and making the learning and academic exchanges easily.Objective : Based on the patients MRI imaging, to develop a simple, objective and reliable three-dimensional MRI classification which can reflect the full three-dimensional informations of the herniated lumbar disc, and then verifying the repeatability and practicality of the new classification.Methods : At first this study reviewed 100 patients with lumbar disc herniation in Department of Orthopaedic Surgery of West China Hospital who had undergone percutaneous endoscopic lumbar discectomy between January 2008 and January 2010.Based on the patients MRI imaging and the technical characteristics of the selected surgical approaches, the three-dimensional MRI classification for herniated lumbar disc had been developed.It consists of three parts: First, in the horizontal plane, in reference to the lumbar disc herniation size,the lesion is described as H1, H2, and H3.Second, in the coronal plane, in reference to the lumbar disc herniation location, the lesion is described as C1, C2, C3 and C4.Third, in the sagittal plane, in reference to the lumbar disc herniation size, the lesion is described as S3, S2, S1, S0, S+l, S+2 and S+3.To test its reliability, a blind review of 50 random patients MRI imaging datas was performed independently by three different examiners using the new classification to verify its repeatability (group differences and difference among within group).According to this new classification, The second group of 100 patients with lumbar disc herniation also had undergone percutaneous endoscopic lumbar discectomy between January 2010 and January 2012.Then the practicality of the new classification was verified after operation (clinical correlation with the surgical approach selection of percutaneous endoscopic lumbar discectomy).Postoperative follow-up: the first group of patients have been followed up for 3-5 years, the second batch of patients have been followed up for 6-30 months.Results : 85% of the first group of patients who had undergone the percutaneous endoscopic lumbar discectomy received the transforaminal approach,15% laminectomy approach.It summarized that transforaminal approach can be apply to almost all types of lumbar disc hemiation patients (especially LA, 5 segment and above);For the L45 and L5S1 patients who have a higher iliac crest or larger transverse process, the inteflaminar approach is more advantages.Based on the experiences in the treatment of the first group of patients as well as the newly developed three-dimensional MRI classification, the second batch of patients who had undergone the percutaneous endoscopic lumbar discectomy (most transforaminal approach) went well, no surgical intervention,and fewer surgical complications.Conclusion : Three-dimensional MRI classification is a simple and practical typing method which can fully reflect the three-dimensional informations of the herniated lumbar disc and as a imaging reference index for the surgical approach selection of percutaneous endoscopic lumbar discectomy.The extent of this typing method,however, may only be applied to the patients with clear herniation boundaries, and do not reflect the degree of disc degeneration as well as the size of the herniation which should be removed in the operation.