Hypophosphatemia in diabetic ketoacidosis is well recognized, but is believed to be usually of moderate severity. We describe 2 patients in whom acute hemolytic anemia secondary to severe (0.19-0.35 mmol/l) hypophosphatemia has developed 1-2 days following treatment for diabetic ketoacidosis. Our experience indicates that severe hypophosphatemia requiring phosphate supplementation does occur in diabetic patients, and calls for increased awareness for the clinical and laboratory manifestations of this complication of diabetic ketoacidosis.