Introduction: Post-operative urinary retention is a common complication of posterior spine surgery for lumbar spinal stenosis. However, it can result in considerable difficulty for the patient, especially when it is severe, as in cases of complete retention. Therefore, it is crucial to consider its risk factors. This report provides a retrospective review of cases with severe post-operative urinary retention with the aim of elucidating its possible risk factors. Case Presentation: Data of five patients with post-operative urinary retention after posterior spine surgery for lumbar spinal stenosis, operated in our facility from 2013 to 2020, were analyzed. Their age, preoperative Japanese Orthopaedic Association ( JOA) score, presence of pre-operative bladder and bowel disorders (BBD), presence of pre-operative muscle weakness, the mean number of vertebral levels operated on, complications such as intraoperative dural tear and hematoma, operative time, estimated blood loss, JOA score in the early post-operative period, and the recovery period for the urinary retention symptoms were examined. The mean pre-operative JOA score was 8.4, and the mean number of operated levels was 2.8. The incidence of pre-operative BBD, pre-operative muscle weakness, intraoperative dural tears, and post-operative hematoma was two each. The mean operative time was 242 min, mean estimated blood loss was 352 g, and the mean JOA score in the early post-operative period was 5.8. The recovery period for urinary retention ranged from 4 days to 9 months postoperatively; one patient also had cervical and thoracic spinal stenosis and underwent decompression of all stenotic levels for relief from complete urinary retention. Conclusion: In our retrospective review of cases with severe post-operative urinary retention after lumbar spinal stenosis surgery, all patients had severe pre-operative symptoms and spinal stenosis at multiple levels. An awareness of potential risk factors and carefully and gently performing the intraoperative procedures can facilitate lesser damage to the spinal nerve. Keywords: Urinary retention, severe preoperative symptoms, hematoma, dural tear, multiple spinal stenosis.