Background: Degenerative lumbar spinal stenosis causes neurological symptoms due to neural compression. Lumbar laminectomy is a commonly used treatment for symptomatic degenerative spinal stenosis. However, it is unknown if and to what extent single level laminectomy affects the range of motion and stiffness of treated and adjacent segments. An increase in range of motion and a decrease in stiffness are possible predictors of post-operative spondylolisthesis or spinal failure. Methods: Twelve cadaveric human lumbar spines were obtained. After preloading, spines were tested in flexionextension, lateral bending, and axial rotation. Subsequently, single level lumbar laminectomy analogous to clinical practice was performedatlevel lumbar2or4. Thereafter, load-deformation tests were repeated. The range of motion and stiffness of treated and adjacent segments were calculated before and after laminectomy. Untreated segments were used as control group. Effects of laminectomy on stiffness and range of motion were tested, separately for treated, adjacent and control segments, using repeated measures analysis of variance. Findings: Range of motion at the level of laminectomy increased significantly for flexion and extension (7.3%), lateral bending (7.5%), and axial rotation (12.2%). Range of motion of adjacent segments was only significantly affected in lateral bending (-7.7%). Stiffness was not affected by laminectomy. Interpretation: The increase in range of motion of 7-12% does not seem to indicate the use of additional instrumentationtostabilize the lumbar spine.Ifinstrumentationisstill consideredina patient, its primary focus should be on re-stabilizing only the treated segment level.