Purpose: To estimate the frequency of iatrogenic injury of major vascular structures during lumbar discectomy. Materials and methods: The medical records of patients who underwent surgery for lumbar disc herniation at our neurosurgical clinic between April 2000 and April 2016 were retrospectively reviewed. Patients with intraoperative iatrogenic vascular injury were identified by reading the surgical notes and the post-operative progress records of patients who had undergone lumbar discectomy. The standard calculation of the incidence of iatrogenic major vascular injury in lumbar discectomy was used to analyse the data. The formula for estimating the standard probability by calculating the incidence rate is: =n/N, where is the estimated probability, n is the number of events and N is the total number of cases. The standard error of this estimate is SE= Results: During the study period, 2498 patients underwent lumbar discectomy at one or more levels of the lumbar spine. The operations were performed by more than 40 different neurosurgeons or surgical residents. More than 95% of the operations were done under a surgical microscope. Two cases were found to have iatrogenic major vascular injuries. The standard frequentist estimate of the probability, (risk-per-case), of iatrogenic major vascular injuries in lumbar discectomy was: =2/2498 = 0.0008 (0.08%). The standard error of this estimate was: ==0.000566 = 10(-4) (5.66) (95% confidence interval for true p = 10(-4) (801)+/-(1.96)x10(-3) (566)). Conclusions: In this study, the incidence of iatrogenic major vascular injuries in lumbar discectomy was 1 in 1249 operations (0.08%). If utmost care is taken, at least some of these iatrogenic intraoperative vascular complications can be avoided or more rapidly treated, and the lives of such patients can be saved.