ObjectiveTo investigate the effect of body mass index (BMI) on the outcome of posterior 360° fusion for single-level lumbar degenerative diseases. MethodsA retrospective study was carried on 302 cases of singlelevel lumbar degenerative diseases treated with posterior 360° fusion between September 2009 and September 2013. All patients were divided into 3 groups according to BMI: normal weight (BMI<24 kg/m2) in 105 cases (group A), overweight (24 kg/m2≤BMI< 28 kg/m2) in 108 cases (group B), and obese (BMI≥28 kg/m2) in 89 cases (group C). There was no significant difference in gender, age, disease duration, disease patterns, affected segments, preoperative Japanese Orthopaedic Association (JOA) score and Oswestry disability index (ODI) among 3 groups (P>0.05). The operation time, intraoperative blood loss, postoperative hospital stay, and complications were recorded. The lumbar function was assessed by JOA score and ODI at pre- and post-operation (at 3, 6, and 24 months). ResultsThe operation time, intraoperative blood loss, and postoperative hospital stay of group C were significantly more than those of groups A and B (P<0.05), but no significant difference was found between group A and group B (P>0.05). The patients were followed up 24-45 months. Postoperative JOA score and ODI showed significant improvements in each group when compared with preoperative ones (P<0.05), but there was no significant difference among groups at each time point after operation (P>0.05). There was no significant difference in the incidence of total complications among 3 groups (χ2=3.288, P=0.193). The incidence of incision-related complications (infection and poor healing) in group C was significantly higher than that of groups A and B (P<0.05), but no significant difference was shown between group A and group B (P>0.05). However, there was no significant difference in cerebrospinal fluid leak, pseudarthrosis formation, and revision among 3 groups (P>0.05). ConclusionPosterior 360° fusion for single-level lumbar degenerative diseases can obtain good effectiveness in patients with different BMI, but patients whose BMI was ≥28 kg/m2 have longer operation time, more intraoperative blood loss, longer hospital stay, and higher incidence of postoperative incision-related complications.