Primary hyperparathyroidism is due to an adenoma in 85% of cases. In 10% of cases, the parathyroid adenoma may be in an ectopic location. Ten per cent of these ectopic adenomas are located in the mediastinum. Imaging modalities performed in persistent or recurrent hyperparathyroidism include ultrasound, MIBI scintigraphy, venous blood sampling, helical CT and MRI. The authors report 3 cases of ectopic adenoma located in the mediastinum, where pre-operative diagnosis was confirmed using cardiac MRI sequences.