The natural history of lumbar disc herniation in conservatively treated patients is not entirely clear. This study was undertaken to clarify the relation between morphologic changes in the herniation and the clinical course. Serial magnetic resonance imaging studies were performed an average of 4.4 times in 30 patients in a 30-month-average period. The Japanese Orthopaedic Association (JOA) score and straight leg raising (SLR) test were improved, with the average reduction ratio of the herniation 15 and 18% on the sagittal and axial images, respectively. The JOA score and SLR test showed the most improvement within 1 year, with little change noted thereafter. In contrast, the disc herniation continued to reduce not only within 1 year, but also thereafter. Patients with progression of disc degeneration showed more marked regression of herniation than those in whom progression was not observed.