Hypercalcaemic crisis is a rare endocrine emergency. Often, an acute renal failure develops due to hypercalcaemia-induced polyuria. The molecular causes comprise stimulation of the calcium-sensing receptor in the ascending Henle loop and a reduced aquaporin expression in the collecting ducts. We report on a 54-year-old woman who was admitted for hypercalcaemic crisis and acute renal failure. Immediate rehydratation, bisphosphonate administration, and slow-extended daily dialysis (SLEDD) were initiated leading to a marked reduction of serum calcium. Endocrine work-up revealed primary hyperparathyroidism due to a parathyroid adenoma, which was treated by emergency surgery. Haemodialysis was continued in the first post-operative weeks for prolonged acute renal failure.