BACKGROUND Hypercalcemia in association with hyperthyroidism is a well-recognized phenomenon. Primary hyperparathyroidism due to parathyroid adenoma in association with thyroid adenoma is extremely rare. These cases can present a diagnostic and therapeutic challenge to the treating physician as the patient may present with symptoms of either disease. METHODS A 47-year-old female patient presented with non-specific complaints including fatigue and muscle cramps. Diagnostic workup revealed significantly elevated plasma calcium levels in association with hyperthyroidism. There was a considerable delay in measuring the parathyroid hormone levels which were significantly elevated. Nuclear medicine studies revealed features consistent with a parathyroid adenoma and a concurrent thyroid adenoma. The patient was rendered euthyroid and subsequently taken to theatre for a thyroid lobectomy and removal of the associated parathyroid adenoma. One year later the patient remains normocalcemic, euthyroid and clinically well. CONCLUSIONS Toxic thyroid adenoma with concurrent parathyroid adenoma and primary hyperparathyroidism is rare. The possibility of primary hyperparathyroidism should be considered where hypercalcemia persists on correcting the hyperthyroidism. Removal of both adenomas will result in cure of the patient.