In order to learn whether patients with diabetic ketosis who had very severe hypertriglyceridemia had underlying genetic hyperlipidemia, the authors measured plasma lipids in 211 episodes. They report the findings in the 15 patients who had initial plasma triglyceride concentrations above 11.3 mmol/L (1,000 mg/dL). These patients were detected during a prospective study of 155 episodes of ketoacidosis and 56 episodes of ketosis. Eleven of the 15 patients had definite or probable insulin-dependent diabetes mellitus (IDDM), but eight of the 15 were not acidemic despite their ketosis. Twelve of the 15 patients (80%) were men, a far higher percentage of men than the 53.6% in the base population of 211 episodes. Plasma triglyceride concentrations returned to normal levels either during the acute episode (seven cases) or well within a year (two more cases) in most of the patients. From that and other considerations, the authors infer that at least ten, and perhaps 12 of the 15 patients did not have an underlying genetic hyperlipidemia contributing to their original severe hypertriglyceridemia. That contrasts with the findings of others who reported that most patients with severe hypertriglyceridemia associated with noninsulin-dependent diabetes mellitus (NIDDM) (usually without ketosis) did have coexisting familial hypertriglyceridemia.