The results and findings in nine cases of ganglion cyst involving the common peroneal nerve indicate that this condition should be kept in mind whenever a patient complains of pain, paresis, or sensory changes in the distribution of the common peroneal nerve or whenever a mass is noted posterolaterally to the head of the fibula. Only two of the nine patients in our series had poor recovery of motor function. Both had noted onset of foot drop at least one year before surgical exploration. The other seven patients with good or excellent recovery of motor function had undergone surgical exploration less than one year after onset of foot drop. At present, there is no substitute for early exploration and excision of the cyst from the nerve.