Schwannoma is the most common tumor of the peripheral nerve sheath. However, there have been few reports on schwannoma of the posterior tibial nerve causing tarsal tunnel syndrome. We report on a 60-year-old man with tarsal tunnel syndrome caused by a schwannoma of the posterior tibial nerve, which was first diagnosed as a ganglion cyst. After enucleation of this tumor, the patient was asymptomatic and had no related sequelae except for minor numbness in the plantar aspects of his digits. Although schwannoma of the posterior tibial nerve is rare, it should be considered even if a ganglion is clinically suspected.