72-year-old woman with a history of primary hyperparathyroidism, for which she underwent surgery years previously, went to see her general practitioner because of a swelling in her neck that had been present for a few months and was growing in size. Other than this she had no symptoms. During the physical examination a solid elastic, non-fixed swelling with a diameter of about 3 cm was palpable on the right of the neck, medially to the sternocleidomastoid muscle. The swelling did not move when she swallowed. Laboratory tests and an MRI scan were suggestive of parathyroid carcinoma. An examination of the neck showed a large, irregular, lobed soft tumour and several small deposits with a yellowish brown appearance. Histology showed no characteristics of malignancy, but showed a picture consistent with the diagnosis of 'parathyromatosis', a rare disorder characterized by hormonally active ectopic parathyroid tissue. Treatment is primarily surgical, aimed at radical resection. Medicinal therapy using a calcimimetic agent may have a role as an adjuvant treatment.