Objective: The most frequent cause of primary hyperparathyroidism are adenomas of the parathyroid gland, the majority of which are composed of chief cells. Oxyphil adenomas are uncommon and account for 3 % of functioning parathyroid adenomas. Up until 1978 year they have been considered non-functional. Method: Laboratory findings revealed calcium levels of 2.86 prior to operation. The serum parathyroid hormone level was 151.40 pg/ml. A CT scan of the neck showed normal size thyroid lobes with heterodense structure with an oval hypodense lesion in the lower right pole of the thyroid. Results: At surgery a mahagony-brown mass measuring 10 mm in diameter was removed and reported as oxyphil adenoma on frozen section. Histopathological examination revealed encapsulated adenoma composed of oxyphil cells with abundant, granular pink cytoplasm and a rim of normal parathyroid tissue. Mitotic figures were absent. Postoperatively, a decrease of the serum calcium down to 2.31 mmol/l was declared. The followup period was unremarkable. Conclusion: There appear to be a growing evidence that a big part of oxyphil adenomas of parathyroid gland can produce parathyroid hormone and contribute to the cases of primary hyperthyroidism.