A well-localized nodular mass near on a tendon is often the first clinical sign of a nodular tenosynovitis or so-called tenosynovial giant cell tumor of the tendon sheath. We report three cases of this rare tumor localized at the lower extremity, in correlation with clinical, radiographic and intraoperative findings. After the pathologic diagnosis was made, the patient in the first case decided not to have the tumor resected. This patient's postoperative course continues uneventfully without expansion of the tumor. In the second and third case, a surgical intervation was performed but both developed a local recurrence. A second operation with partial resection of the tendon was successfully performed. To the last follow-up 12 and 24 months after revisions, there were no signs of local recurrence. The review of the literature shows that treatment modalities for such lesions range from excisional biopsy to radiation therapy. The authors present their own experience with the MRI diagnosis and the therapy. Using well-defined histopathologic criteria, marginal resection is the treatment of choice. To prevent a local recurrence, partial resection of the tendon should be done during the primary surgery.