Hyperosmolar hyperglycemic nonketotic diabetic coma after cardiac operations was reviewed in a total of 12 patients from the literature and from my experience in an attempt to determine the clinical features of this condition. Among the unique features of this disease were the following: The mortality is high (42%). The morbidity and mortality are higher in patients with no previous history of diabetes mellitus (67% and 50%) than in those with such a history (33% and 25%). Polyuria is usually a heralding symptom. There is an average time lag of 6 days between the onset of polyuria and the established diagnosis of hyperosmolar hyperglycemic nonketotic diabetic coma. The time lag in patients who died was 7.5 +/- 0.8 days (mean +/- standard error of the mean), significantly longer than in survivors (4.5 +/- 0.8 days). Polyuria usually emerges after the stormy immediate postoperative days have passed (on postoperative day 5.3 on the average). Polyuria is generally regarded as a favorable sign not suggestive of complicating hyperosmolar hyperglycemic nonketotic diabetic coma. Therapies known to precipitate this disorder are continued even after development of polyuria. Gastrointestinal bleeding can be a precipitating factor. Hyperalimentation or elemental diet may cause dehydration and trigger hyperosmolar hyperglycemic nonketotic diabetic coma. A high or rising serum sodium concentration and/or blood urea nitrogen level with polyuria may be a warning sign of this complication. Too hasty correction of the hyperosmolar state can be dangerous. Pulmonary dysfunction may be involved in the symptoms of hyperosmolar hyperglycemic nonketotic diabetic coma.