INTRODUCTION: Intrathyroidal parathyroid adenomas (IPA) are a not an uncommon cause of persistent hyperparathyroidism. There is no consensus on their prevalence, embryological origin and position within the thyroid. PATIENTS AND METHOD: Retrospective review of prospectively recorded surgical protocols of patients having had parathyroidectomy for primary (n = 437) or secondary (n = 137) hyperparathyroidism by the same surgeon. Cases with IPA were identified and the following data were recorded: age, most probable embryological origin, position within the thyroid (side and height), results of imaging techniques and surgical implications. RESULTS: Seventeen IPA were detected in 16 patients (6M, 10F, prevalence 3.2%); 9 belonged to IIIP and 8 to IVP. Three lower IPA were supernumerary glands. Eight IPA were included within the right lower thyroid lobe. Twelve IPA (70.6%), were found during the initial parathyroidectomy: 3 were enucleated and 9 were treated with a partial thyroidectomy or hemithyroidectomy. Of the 3 enucleations, 2 had a local benign recurrence due to an incomplete capsule resection. No patients treated with thyroidectomy had a recurrence. The remaining 5 IPA, found in 4 patients, were not identified initially and caused persistence of the disease leading to 5 reinterventions. CONCLUSIONS: IPA are present in 3% of patients submitted to parathyroidectomy. They predominate in the right thyroid lobe and can be IIIP, IVP and supernumerary. They often cause persistence. Thyroid resection affords the best results since complete enucleation can be difficult and leaving behind a fragment of the IPA results in local recurrence.