Objective To investigate the effectiveness of surgical treatment for single-level degenerative lumbar instabil ity (DLI) by comparing traditional open transforaminal lumbar interbody fusion (TLIF) with minimally invasive TLIF. Methods Between March 2007 and May 2009，87 patients with single-level DLI were treated by traditional open TLIF (group A, n=45) and by minimally invasive TLIF (group B, n=42), respectively. There was no significant difference in gender, age, disease duration, segment level, combined diseases of lumbar spine, or the proportion of uni- and bilateral symptom between 2groups (P gt; 0.05). The indexes of surgical trauma，systemic inflammatory response, cl inical outcomes, and aravertebral muscle injury were compared between 2 groups. Results Operation was performed successfully in all patients. The patients were followed up 2.9 years on average in group A and 2.8 years on average in group B. The incision, blood loss, and postoperative drainage in group B were significantly less than those in group A (P lt; 0.05), but the operation time in group B was significantly longer than that in group A (P lt; 0.05). There were significant differences (P lt; 0.05) in C-reactive protein, leucocyte count, and creatine kinase MM between 2 groups at 24 hours postoperatively as well as in C-reactive protein at 6 days postoperatively; group B was superior to group A. At last follow-up, the Oswestry disabil ity index (ODI) and visual analogue score (VAS) were significantly improved when compared with the preoperative scores in 2 groups (P lt; 0.05). There were significant differences in ODI and back pain VAS score (P lt; 0.05), but no significant difference in leg pain VAS score (P gt; 0.05) between 2 groups. At last follow-up, no low back pain occurred in 8 and 18 cases, mild in 25 and 18 cases, moderate in 9 and 6 cases, and severe in 3 and 0 cases in groups A and B, respectively, showing that low back pain was significantly l ighter in group B than in group A (Z= —2.574, P=0.010). At last follow-up, the atrophy ratio of multifidus muscle was 37% ± 13% in group A and was 15% ± 7% in group B, showing significant difference (t=12.674, P=0.000). The multifidus muscle atrophy was rated as grade I in 18 and 44 sides, as grade II in 42 and 32 sides, and as grade III in 30 and 8 sides in groups A and B, respectively, showing significant difference (Z= — 4.947, P=0.000). Conclusion Both traditional open TLIF and minimally invasive TLIF are the effective treatments for single-level DLI. Minimally invasive TLIF has less surgical trauma, sl ighter postoperative systemic inflammatory response, less paravertebral muscle injury, and lower incidence of postoperative back pain, but it has longer operation time.