Calciphylaxis is a dreaded complication of renal failure characterized by nodular subcutaneous calcification and painful tissue necrosis often leading to ulceration, secondary infection, and high mortality rates. The case of a woman receiving continuous ambulatory peritoneal dialysis who had a typical clinical presentation of calciphylaxis confirmed by x-ray and technetium scan findings is described. After nonresponse to conventional therapy, treatment with intravenous sodium thiosulfate 3 times weekly was begun, and she had rapid and dramatic relief of signs and symptoms and improvement of technetium scans. Prolonged treatment was well tolerated without serious side effects and accompanied by continued clinical improvement.