Background: Tarsal tunnel syndrome (TTS) is an entrapment neuropathy that occurs in the ankle. Previous studies reported that this disease was due to physiologic factors and structural lesions in the ankle or foot. The authors investigated the causative factors of TTS and their frequency via operative findings. The diagnostic value of MRI was also evaluated based on the concordance between the operative findings and the MRI findings. Methods: This study was performed in retrospective by using medical record of the patients who underwent operations with TTS from August 2003 to May 2010. Physical examination, nerve conduction study, and MRI were conducted on patients who visited department of neurology or orthopedic surgery due to pain and sensory abnormality of their ankle and foot. Results: 34 patients underwent the operation. Ganglion accounted for the largest portion of the operative findings. In addition, varicose veins, intrinsic foot muscle hypertrophy, tenosynovitis, and fascia thickening were mainly observed. Of the 34 patients, 33 patients underwent pre-operative MRI, of whom 18 patients showed MRI findings consistent with the operative findings. Conclusions: Space-occupying lesions accounted for the majority of the causative factors in TTS patients who underwent the surgical treatment. In this study, the MRI appeared useful for identifying causes of TTS.