Objective To summarize the efficacy of percutaneous endoscopic transforaminal unilateral decompression for the treatment of lumbar spinal stenosis, and to investigate the incidence and possible reasons for lower extremity symptoms of non-surgical side after surgery. Methods The clinical data of 46 patients who underwent percutaneous endoscopic transforaminal unilateral decompression for lumbar lateral recess stenosis between February 2016 and March 2018 were retrospectively analysed. There were 22 males and 24 females with an average age of 56.9 years (range, 21-90 years). The disease duration was 6 months to 12 years (mean, 4.8 years). There were 37 cases of single-segment lumbar lateral recess stenosis and 9 cases of multi-segment stenosis. All patients underwent single-segment surgery, including 2 cases of L3, 4, 35 cases of L4, 5, and 9 cases of L5, S1. For patients with multi-segment lumbar lateral recess stenosis, the single segment consistent with radicular symptom was selected for surgery. The visual analogue scale (VAS) scores of low back pain and sciatica and Oswestry disability index (ODI) scores were recorded preoperatively and at last follow-up to evaluate the relief of symptoms. Postoperative symptoms on non-surgical side of lower extremity including new or aggravated radiation pain and numbness were recorded. The surgical effectiveness was evaluated according to modified MacNab score at last follow-up. Results All the 46 patients underwent successful operations without postoperative complications such as wound infection, permanent nerve root injury, and deep vein thrombosis. The patients were followed up 12-37 months (mean, 23.8 months). Four patients suffered from radioactive pain and numbness for the non-surgical side of lower extremities at 1-3 months postoperatively, and the symptoms were improved after conservative treatment without revision surgery. VAS scores of low back pain and sciatica and the ODI scores were significantly improved at last follow-up when compared with preoperative ones (P<0.01). According to the criteria of modified MacNab scores, 25 cases were excellent, 17 cases were good, 3 cases were fair, and 1 case was poor. The excellent and good rate was 91.3%. Conclusion Percutaneous endoscopic transforaminal unilateral decompression for lumbar spinal stenosis would be able to relieve pain effectively and achieve good results. Lower extremity symptoms of non-surgical side may be observed postoperatively. Although the symptoms can be relieved by conservative treatment, further investigation should be carried out for the long-term result of those cases.