Aim:Oblique lateral interbody fusion (OLIF) is a minimally invasive surgical method that can access lumbar spine without direct dissection of psoas muscle and the need for intraoperative neuromonitoring (IOM) is questionable. The purpose of this study is to examine and document the transient and persistent perioperative complications in patients who underwent OLIF for degenerative lumbar disease without IOM. Material and Methods:Total 129 consecutive patients who were diagnosed as degenerative spinal disease from L1 to S1 and underwent the mini-open OLIF, were identified and retrospectively reviewed. All patients were classified as two group; non-IOM group and IOM group. According to the relation to surgical procedure, the complications were divided into two group; ‘procedure-related’ and ‘procedure-unrelated’. Based on the effect of duration, the complications were defined as ‘transient’; symptom relieve within 30 days postoperatively, and ‘persistent’; symptom remain more than 30 days postoperatively. Results:The study groups comprised 57 cases in the IOM group and 72 in the non-IOM group. The IOM group showed of 24.6% (transient; 17.6%, persistent; 7.0%) of complications, and the non-IOM group 29.2% (transient; 25.0%, persistent; 4.2%). Incidence of postoperative leg symptoms related lumbar plexus and/or psoas muscle injury was shown as 6 transient and 3 persistent in the IOM group (overall 15.3%), and 12 transient and 3 persistent in the non-IOM group (overall 20.9%). Conclusion:This comparative study verifies that the mini-open OLIF could be safely carried out without aid of the IOM.