The authors have experienced 30 cases of herniated nucleus pulposus(HNP) of the lumbar spine which were developed in children and adolescents, under 18 years old and followed up for more than 1 year since September, 1983. Summary of the clinical analysis upon these cases are as follows: 1. There were 18 males and 12 females. The age of the youngest patients was 10 year 2 month old. 2. The incidence was 3.9% (30/756 cases) of all patients with HNP. 3. There were no history of significant trauma but 12 patients(40%) were related with athletic activities. 4. Mechanical tension such as positive S.L.R. test, positive Lasegue's sign are present in all cases but neurologic signs which include changes in sensation, muscle weakness were present less than half. 5. Among the 30 patients, 27 patients had disc protrusions at L4-5, 2 patients at L5-Sl and 1 patient at L3-L4. 6. Among the 30 patients, 13 patients(43.3%) were treated conservatively and 17 patients(56.7%) operatively. 7. According to Naylor's assessment, excellent were in 23 cases(76.7%), good in 3 cases(10.0%), fair in 2 cases(6.7%) operatively. 7. According to Naylor's assessment, excellent were in 23 cases(76.7%), good in 3 cases(10.0%), fair in 2 cases(6.7%) and 2 poor cases(6.7%). 8. The patients tolerate surgery extremely well and the results were excellent.