An athletic patient presented with a nontraumatic peroneal neuropathy that failed to resolve after a period of rest. A magnetic resonance image (MRI) showed a multilobulated mass in the course of the common peroneal nerve consistent with a plexiform neurofibroma. Surgical exploration revealed a mass, which coursed from the midthigh to the fibular neck, that was intimately involved with the fibers of the nerve bundle and had cystic degeneration with vesicles along its length. The authors recommend MRI as highly accurate in diagnosing unusual causes of peroneal neuropathy.