METHODS Fifty-six patients with lumbar disc herniation who had participated in a double-blind study comparing chymopapain with saline were invited to undergo a magnetic resonance imaging assessment of the lumbosacral spine more than 10 years later. OBJECTIVE The aim of this study was to assess the long-term morphologic changes after treatment of disc herniation by chemonucleolysis and laminectomy and to compare these findings with the natural history of the disorder. BACKGROUND There is little information on the effects of different treatment methods for lumbar disc herniation on the long-term morphologic changes in the disc. METHODS Of the original 56 patients, 39 were entered into the study: 12 had been treated by saline injection alone, 14 by chemonucleolysis alone, and 13 had subsequently required laminectomy for a failed intradiscal injection. Each sequence of magnetic resonance images was examined by a radiologist who was unaware of the treatment given. The signal strength was assessed on T2-weighted images in the sagittal plane and disc morphology on T1- and T2-weighted sagittal and T1-weighted axial images. RESULTS The signal of the treated disc was absent in all cases in each group. Thirty-seven percent of patients were found to have a persistent herniated disc and the incidence was similar in all three treatment groups. The presence or absence of herniation at 10 years had no significant bearing on a successful outcome. CONCLUSIONS The findings of this study indicate that long-term improvement of a patient's symptoms after treatment of disc herniation may occur with or without resolution of the hernia. This and the similar morphologic findings in the different groups is consistent with the 10-year clinical results after the treatment of disc herniation reported by Weber.