An automated percutaneous lumbar discectomy(APLD) have been apphed for contained lumbar disc herniation. But suggested that more exclusion criteria than disc containment was needed to improve success rate. The purposes of this study are to evaluate cIinical outcome of more than 4 years follow up of APLD, to analysis the cause of failure for longer follow up period, and to define prognostic factor of APLD. The l04 patients with contained lumbar disc herniation were treated with APLD from March 1990 to November 1992 in National Medical Center. The surgical candidates were contained focal disc herniation in MRI, sciatica than back pain, failure to conservative management at least 6 weeks and clinical and radiological correlation. And patient were excluded from this data if they had history of previous lumbar surgery and compensation claims. Among them 74 cases were followed up for over 4 years (Mean: 5.3 years). The results were accessed by questionnaire using telephone or OPD follow up. The overall success rate was 84% on 3 months follow up, but 68.9% on more than 4 years follow up by four subjective criterias (Onik, 1987). Causes of decreasing success rate were reoperation, recurrence without specific cause or after sprain and heavy work. 76% of failed cases occurred within 1 year and 40% of them underwent open discectomy. The patient sex, treated level, duration of symptom were not influenced on success rate, but age was factor related to success rate. In this study we can assess the effectiveness of APLD within 3 months in most cases and then change treatment option according to patients status, and it seems that we need more exclusion criteria than disc containment in MRI and refined patient selection in order to decrease the failures.