In a prospective, consecutive study 93 patients who had had previous lumbar spinal surgery underwent repeat decompression for persistent or recurrent back and leg pain. The previous operations had been discectomies in 65 patients and decompression for spinal stenosis in 28; two of the latter group had also had posterolateral fusion. At the repeat operation, disc herniation was found in 19 patients, lateral spinal stenosis in 19, central spinal stenosis in 20 and periradicular fibrosis in 35. Ninety-one patients were followed up for two years after surgery; the effect of the operation was recorded using a four-scale grading system. The results were significantly related to the diagnosis. Nerve-root compression due to recurrent disc herniation or to bony compression responded well to repeat decompression. In patients with a single nerve-root compression the results were similar to those obtained in primary operations. Sciatica due to nerve-root scarring was seldom improved by the repeat operation.