An 80-year-old woman with a history of bilateral breast cancer was referred for investigation of hypercalcaemia, initially suspected to be bone metastasis. Sestamibi scan revealed the cause to be a large parathyroid adenoma which was then removed. Hypercalcaemia is the most frequent metabolic complication of breast cancer. Primary hyperparathyroidism is one of the most frequent causes of benign hypercalcaemia, but is often not considered in oncology patients. This case illustrates the importance of considering two primary pathologies.