PURPOSE: The purpose of this study was to evaluate the radiologic findings of lumbosacral transitional verte-brae (LSTV), as seen on plain radiographs and MRI, and to compare the incidence of combined diseases be-tween unilateral and bilateral groups. MATERIALS AND METHODS:We retrospectively evaluated the plain radiographs and MR images of 63 patients with LSTV, classifying its type according to Castellvi 's criteria, and evaluated disc herniations, facet joint os-teoarthritic change, scoliosis, and spondylolisthesis. We then compared the incidence of each combined diseases between unilateral and bilateral groups, and as a control group, 63 patients without LSTV were also eval-uated. RESULTS: Forty of 63 cases of LSTV (63.5%) were bilateral, and 23 (36.5%) unilateral. According to Castellvi 's criteria, the incidence of type I was 41.3% (unilateral 7 cases, bilateral 19), type III30.2% (unilateral 8 cases, bilateral 11), type II23.8% (unilateral 8 cases, bilateral 7), and type IV 4.8% (unilateral 0 cases, bilateral 3).With combined diseases, the incidence of disc herniation was 66.7% (unilateral 15 cases, bilateral 27), moderate to severe facet joint osteoarthritic change 28.6% (unilateral 11 cases, bilateral 7), scoliosis 27.0% (unilateral 9 cases, bilateral 8), and spondylolisthesis 9.5% (unilateral 2 cases, bilateral 4). The incidence of facet joint os-teoarthritic change was significantly higher in the unilateral group (47.8%) than in the bilateral group (17.5%) (p=0.02), and scoliosis occurred at a higher rate in the unilateral group (39.1%) than in the bilateral group (20.0%) (p=0.18). There was, however, no significant difference in the incidence of disc herniation and spondylolisthesis between the two groups (unilateral group: 65.2% and 8.7%; bilateral group: 67.5% and 10.0%, respectively). CONCLUSION: With LSTV, the incidence of facet joint osteoarthritic change was significantly higher in the unilat-eral group than in the bilateral group, and scoliosis also showed a higher rate of occurrence in the unilateral group.