Objective: The objective of this study is to analyze incidence, estimate cost savings, and evaluate best management practices of complications resulting from outpatient transforaminal endoscopic decompression surgery for lumbar foraminal and lateral recess stenosis performed in an ambulatory surgery center. Background: Endoscopic spinal surgery is gaining popularity for the treatment of lumbar disc herniations. Recent advances in surgical techniques allow for endoscopically assisted bony decompression for neurogenic claudication symptoms due to spinal stenosis. Postoperative complications from dural tears, recurrent disc herniations, nerve root injuries, foot drop, and facet and pedicle fractures, and postoperative sequelae such as dysesthetic leg pain and infiltration of the surgical access and spinal canal with irrigation fluid causing spinal headaches and painful wound swelling, as well as failure to cure, have been reported. Methods: A retrospective study of 1839 consecutive patients with an average mean follow up of 33 months (range: 24 to 85 months) that underwent transforaminal endoscopic decompression surgery at 2076 levels between 2006 and 2015 was conducted to analyze incidence, and estimate the cost savings of postoperative adverse events following endoscopic foraminotomy and microdiscectomy. Complications were stratified using Dindo's 7-category grading system, distinguishing them from procedure-inherent sequelae as well as failure to cure. Only patients with unilateral radiculopathy due to either herniated disc or lateral recess stenosis were included in this study. Preoperatively, disc migration was graded by direction and distance from the disc space according to Lee's radiologic 4-zone classification. The type of disc herniation was classified either as contained or extruded. Contained herniations were further subclassified as disc protrusions versus disc bulges. In addition, the preoperative disc height was recorded. Bony spinal foraminal stenosis and lateral recess stenosis were graded on preoperative magnetic resonance imaging and computed tomography scans into mild, moderate, and severe by dividing the lumbar neuroforamen into 3 zones: (1) entry zone, (2) midzone, and (3) exit zone. Surgical outcomes were classified according to the Macnab criteria. In addition, reduction in the visual analog scale (VAS) scores were assessed. Results: According to the Macnab criteria, excellent and good results were obtained in 82.2% of patients with extruded disc fragment (331/1839). In this group, the mean VAS score decreased from 5.9 6 2.5 preoperatively to 2.4 6 1.8 at final follow-up (P , .01). Patients with contained disc herniations (648/1839) had excellent and good results 72.7% of the time. In this group, the mean VAS score decreased from 7.2 6 1.6 preoperatively to 3.1 6 1.5 at final follow-up (P , .01). In the spinal stenosis group (860/1839), 75% of patients had excellent to good results. Postoperative grade I complications (any deviation from normal postoperative course treated with observation) o...