Fifty-three cases of isthmic spondylolisthesis were treated with distraction rod instrumentation and posterolateral fusion with or without nerve root decompression, and they were followed for an average of 39 months. Thirty-one cases without neurologic deficit were treated with instrumentation and fusion only. In 22 cases of predominant sciatic pain with neurologic deficit signs, nerve root decompression and instrumentation with fusion were conducted. The results showed a 90.6% solid union rate with satisfactory clinical improvement. Realignment of the vertebral displacement such as reduction of olisthesis and widening of the olisthetic disc spaces was obtained to some extent. No serious complications were encountered.