Calciphylaxis is a rare, severe complication of secondary hyperparathyroidism. Patients present with painful, violaceous, mottled skin lesions of the upper and lower extremities, which become necrotic and produce nonhealing ulcers. Gangrene of fingers and toes frequently requires amputation, produces nonhealing wounds, and can lead to sepsis and death. We reviewed the clinical course of five patients with calciphylaxis treated in our institution. The three men and two women (aged 47 to 72 years) had secondary hyperparathyroidism from chronic renal failure. All patients had severe pruritus, painful ulcers, and severe hyperphosphatemia with elevated serum calcium-phosphate product (greater than 12 mmol2/L2), but the serum parathyroid hormone levels were only moderately elevated. Most patients had medical calcification of medium and small blood vessels, and some had soft-tissue calcification visible on roentgenography. Treatment consisted of local wound care, antibiotics, phosphate-binding agents, and parathyroidectomy. Two patients died of uncontrollable sepsis. The three survivors had dramatic improvement of pain and ulcers after parathyroidectomy. Calciphylaxis is a limb- and life-threatening complication of secondary hyperparathyroidism. Diagnosis can be made by recognizing the characteristic painful skin lesions, ulcers, and gangrene of the digits, and patients should be treated with subtotal parathyroidectomy.