Abstract Background Non-functioning parathyroid carcinoma is an extremely rare malignancy among endocrine tumors. We report a case in which non-functional oxyphilic parathyroid carcinoma was diagnosed from clinical symptoms and pathological diagnosis. Case presentation The patient was a 42-year-old man with no medical or family history of note. He had presented to a local hospital with a neck mass 2 months earlier. Medullary thyroid carcinoma was diagnosed and he was referred to our department. A 3.5-cm mass was observed in the left thyroid lobe. Laboratory data for thyroid functions, thyroglobulin, anti-thyroglobulin antibodies, anti-thyroid peroxidase antibodies, serum calcium, and parathyroid hormone (PTH) were all within normal ranges. Ultrasonography revealed a 40-mm irregular, hypoechoic mass throughout the left thyroid lobe. Follicular thyroid tumor was suspected from fine-needle aspiration cytology. Left lobectomy was performed. Pathological features revealed a thick fibrous capsule around the tumor, and a thick fibrous band was observed inside the tumor. Both capsular invasions and vascular invasions were observed. Tumor cells were eosinophilic and displayed solid growth. Immunohistochemically, tumor cells were negative for thyroid transcription factor-1, negative for thyroglobulin, negative for chromogranin A (positive for normal parathyroid tissue within the nodule), positive for PTH, and positive for parafibromin. Ki-67 labeling index was 10%. Based on these findings, non-functional oxyphilic parathyroid carcinoma was diagnosed. One and a half years postoperatively, calcium and PTH were within normal ranges, and he has shown no evidence of recurrence or metastasis. Conclusions Non-functioning oxyphilic parathyroid carcinoma is an extremely rare malignancy, and definitive diagnosis is difficult to obtain preoperatively. Few reports have been made worldwide, and information on the long-term prognosis is scarce. Long-term surveillance by imaging is mandatory, since no indices that can be used as a marker for postoperative recurrence and metastasis have been identified.