A common peroneal nerve palsy caused by a ganglion cyst is a rare entity. A
48-year old man was referred with a six year history of intermittent pain
that had resulted in a complete palsy of the common peroneal nerve. A magne
tic resonance (MR) scan showed compression of the nerve by a ganglion, whic
h was excised and the nerve was released. Three months later the lost muscl
e function had returned completely.