Aim: Evaluate the preoperative prognostic factors of a poor result in conventional surgery of lumbar disc herniation. Methods: From November 1995 to November 2001, we performed 113 standard discectomies (63 males/50 females) with a mean-age of 42 years (21–75). All patients had been evaluated preoperatively with X-ray and C.T. scan. Fifty-nine patients (52%) had a preoperative M.R.I., and an evaluation was made of disk degeneration degree, multilevel degeneration and bone changes in vertebral end-plates (according Modic classiþcation). The postoperative mean follow-up was 46,2 months. The outcomes were evaluated considering the reoperation rate, the intensity of pain in the Visual Analogue Score, and þnal function with the Oswestry Disability Index. The results were compared using ANOVA. Results: We have found a statistical correlation between a poor result and older age (p=0.006), diabetes (p=0.005), psychological factors (p=0.006) and preoperative X-ray changes, such as disk height loss greater than a third (p< 0.001), subcondral sclerosis (p< 0.001), segmental instability (p=0.019) and ostheo-arthritis (p< 0.001). Regarding M.R.I., the multilevel degeneration and the Modic changes (type I, II or III) have been correlated in this study with poor functional result (p=0.004 and p< 0.001 respectively). Conclusions: Our results support the concept that in patients with lumbar disk herniation and with described X-ray or M.R.I. changes, especially changes in vertebral end-plate, we should strongly consider treatment for disk degeneration and not limit the intervention to the excision of disk extrusion.