This study evaluates the effect of internal neurolysis on a chronically compressed primate median nerve as compared with a simple decompression procedure. In 11 adult, cynomologous monkeys, the median nerve in the carpal tunnel was banded with a silicone tube. After 6 months of nerve compression (mild to moderate compression in our model) in eight monkeys, a microneurosurgical internal neurolysis was carried out on the median nerve of one hand and a simple decompression (removal of band) was carried out on the median nerve of the other hand. Histologie, morphologic, and electrophysiologic evaluation was carried out 6 months later. Six control animals were similarly evaluated after 0, 6, and 12 months of nerve compression. The degree of compression produced was not severe in that it did not cause Wallerian degeneration. Histologie and electrophysiologic improvement was produced in both treatment groups over the two chronically compressed groups (6 and 12 months of compression). While internal neurolysis did not cause intraneural scarring or nerve fiber damage as compared with simple decompression alone, there was no difference noted between the effects of these two treatment methods on the chronically compressed nerve.