We report a case of extreme hypercalcaemia associated with a parathyroid adenoma in a young man. The patient presented with classical symptoms of a hypercalcaemic syndrome, and serum calcium and parathyroid hormone levels were 6.92 mmol L(-1) and 70.2 pmol L(-1) respectively. After stabilizing the patient and reducing the calcium level, a parathyroidectomy was performed. The postoperative course was uneventful with rapidly resolving clinical symptoms. Hypercalcaemic crisis is a rare but life-threatening complication of primary hyperparathyroidism. It should be suspected in acutely ill patients complaining of muscular weakness, gastrointestinal and cerebral symptoms. To reduce mortality, it is essential to correctly diagnose the condition without delay and provide appropriate emergency management correcting hypercalcaemia and dehydration. Successful parathyroidectomy quickly relieves symptoms and prevents recurrence.