We describe a primitive hyperparathyroidy in a old woman due to a parathyroid adenoma localisated by Technetium 99m, Thallium 201 scintigraphy within the thyroid gland. During surgery, this adenoma was found inside a thyroid adenoma. It is the second case reported on the literrature in a such localization. We underline the interest of the scintigraphy Technetium 99 m, Thallium 201, for the detection of ectopic parathyroid adenoma.