To investigate the effectiveness and safety of microendoscopic decompression via unilateral approach for lumbar spinal stenosis. Methods Between May 2006 and June 2009, 79 patients with lumbar stenosis were treated and divided into 2 groups: posterior lamina fenestration decompression (group A, n=37), endoscopic decompression via unilateral approach (group B, n=42). There was no significant difference in age, sex, segment level, and disease duration between 2 groups (P gt; 0.05). The cl inical outcomes were assessed by using the visual analogue scale (VAS) score and Oswestry Disabil ity Index (ODI). The operation time, blood loss, compl ications were compared between 2 groups. Results Operations were successfully performed in all cases. The operation time, blood loss, and drainage volume were (75.0 ± 25.7) minutes, (140.3 ± 54.8) mL, and (46.5 ± 19.7) mL in group A, were (50.4 ± 18.2) minutes, (80.2 ± 35.7) mL, and (12.7 ± 5.3) mL in group B; there were significant differences between 2 groups (P lt; 0.05). All the wounds healed by first intention. All patients were followed up 12-39 months (mean, 16 months). In group A, 1 patient suffered from intervertebral space infection after operation and recovered after conservative treatment; 4 patients had lumbar instabil ity after operation and recovered after lumbar interbody fusion combined with spine system internal fixation. In group B, 2 patients suffered from spinal dural rupture during operation and recovered after corresponding treatment, and no lumbar instabil ity was found. There was no significant difference in VAS score and ODI between 2 groups at preoperation (P gt; 0.05). Both VAS score and ODI were significantly improved at early stage after operation and last follow-up when compared with preoperation in each group (P lt; 0.05). Comparing with group A, there was significant improvement in VAS score at 24 hours postoperatively and in ODI at 1 month postoperatively in group B (P lt; 0.05), but no significant difference was observed at last follow-up (P gt; 0.05). According to cl inical evaluation of ODI mprovement rate, the excellent and good rate was 89.2% in group A and 92.9% in group B, showing no significant difference (χ2=0.896, P=0.827). Conclusion Comparing with posterior decompression surgery, microendoscopic decompression via unilateral approach is one of effective method to treat lumbar stenosis, with less trauma of fenestration yield and good early outcomes.