Aim:Lumbar spondylolisthesis is a common cause of disabling leg and back pain. A detailed preoperative radiological evaluation is essential to define the best surgical approach, such as the need for instrumentation or simple neurological decompression. The objective of this study is to correlate the main findings in lumbar X-ray, MRI and to identify factors that determine instability.Material and Methods:Retrospective and observational study of patients with confirmed diagnosis of lumbar or lumbosacral low grade spondylolisthesis at a single level. Preoperative X-ray and MRI were evaluated. Statistical analysis was performed using Fisher\'s exact test and Kappa statistics.Results:59 patients were included. 62% of the patients had Modic changes in the MRI. Degenerative and isthmic spondylolisthesis was found in 49.2% and 50.8, respectively. All patients had degenerative disc changes at the level of the listesis. 18 (30,5%) and 3 (5,1%) patients had moderately and severely asymmetrical facets, respectively. 64,4% had neutral facets. Dynamic X-ray detected mobility in 52.5% of the cases. There was a negative correlation between the presence of tropism, mobility (p = 0.03) and present facet tropism (p = 0.02). Substantial agreement (91.52%) between MRI and X-ray was found [Kappa 0,81 (0,66;0,97)].Conclusion:MRI was sufficient for the diagnosis of lumbar spondylolisthesis and dynamic lumbar Rx was important to define segmental mobility. In addition, facet tropism had a protective effect for instability.