BACKGROUND CONTEXT Lumbar intervertebral disc herniation (LIDH) is known to be a key cause of sciatica. Previously we found a significant limitation of neural displacement (66.6%) with the straight leg raise test (SLR) on the symptomatic side of patients with sub-acute single level posterolateral LIDH. PURPOSE To ascertain if changes incord excursion with SLR at 1.5-year follow-up time accompany changes in clinicalsymptoms. STUDY DESIGN/SETTING Controlled radiological study. PATIENT SAMPLE Follow-up study on 15 patients with significant sciatic symptoms due to a single level posterolateral LIDH. OUTCOME MEASURES Conus medullaris displacement was quantified reliably with a randomized procedure during the unilateral and bilateral SLR and results compared both between maneuvers and with baseline data. LIDH was examined with 1.5T Magnetic Resonance Imaging (MRI) scannerusing different scanning sequences for planning and for measurement purposes, while low back pain (LBP) and radicular symptoms were assessed during clinical examination with visual analogic scales. METHODS The patients were re-assessed clinically and radiologically with a 1.5T MRI scanner at 1.5-year follow-up. Displacement of the conus medullaris with the unilateral and bilateral SLR was quantified with a randomized procedure and compared between SLRs and to data from baseline. Multivariate regression models and backward variable selection method were employed to identify variables associated with the patients’ symptoms. RESULTS Conus medullaris caudal displacement in response to SLRs increased significantly in all the tested subjects. Compared to baseline values, the data showed a large increase in neural sliding with the symptomatic SLR (323.4%, 2.52mm, p≤.001), 37.1% with asymptomatic SLR (0.82mm, p=.0058) and 48.2% with bilateral SLR (1.64mm, p≤.001). Increase in neural sliding correlated significantly with the resolution of radicular symptoms in the ipsilateral limb (Pearson=−0.719, p≤.001) and low back pain (LBP) (Pearson=−0.693, p≤.001). Backward variable selection method indicated improvement of neural sliding (p=.004) and degrees of hip flexion with symptomatic SLR (p=.025) as the main variables being associated with improvement of radicular pain. Reduction of LBP showed to be associated with improvement of neural sliding (p=.006). Overall, there was an average increase in neural sliding of 230.7% (symptomatic, asymptomatic and bilateral SLRs) in association with decrease of symptoms during the follow-up period. This improvement of neural sliding was found to be associated with 74.7% decrease in self-reported LBP symptoms on visual analog scale (VAS), as well as 76.0% decrease in self-reported radicular symptoms on VAS. CONCLUSIONS This study shows a significant association between the improvement of neural adaptive movement with the SLR and resolution of both radicular and LBP symptoms in patients with posterolateral LIDH during 1.5-year follow-up time. To our knowledge, these are the first noninvasive data to objectively support the association between magnitude of neural adaptive movement and improvement of clinical symptoms in in-vivo and structurally intact human subjects. The data also gives new and valuable insights into our understanding of the mechanisms of the SLR test.