To analyze the post-operative clinical results of lumbar microdiscectomy with respect to time, and to evaluate the causes of fail-ure by survivor ship analysis.

The clinical results of 162 patients were evaluated using MacNab's criteria and the survival rate was analyzed by using Kaplan-Meier survivor ship analysis. Several factors suspected of influencing survival were evaluated.

Survival was 93.7% at 12 months after the operation, and showed annual decrements to reach 84.7% at 60 months but did not change thereafter until the final follow up. There were total 18 failed cases and the failure rate after 5 years was 0%. Statistically significant factors influencing the survival rate were, the type and level of disc herniation. The causes of early failure, which occurred within 12 months of surgery, were usually due to residual or recurrent radiating pain, whereas the major cause of late failure, which occurred after 12 months, was usually residual back pain.

The failure rate was relatively high during the early post-operative period, but this decreased with time. Since long-term survival was relatively high, lumbar microdiscectomy could be considered an effective and satisfactory surgical technique.