Hypertriglyceridemia is the most frequent lipid abnormality associated with obesity. Genetic polymorphism of apolipoprotein E (apoE) has been demonstrated to influence lipid levels. We wanted to assess the role of apoE alleles in the hypertriglyceridemias of the obese population. The apoE phenotypes and lipid status were investigated in a population of 172 obese French subjects. The frequencies of phenotypes E4/3, E4/4 and E4/2 were 29.7%, 8.1% and 2.1%, respectively, in a subgroup with triglycerides greater than or equal to 200 mg/dl (n = 37) versus 14.2%, 2.7% and 0.9% in the normolipidemic subgroup (p less than 0.005). The odds ratio of hypertriglyceridemia was 3.15 for obese subjects with epsilon 4; 27.7% of hypertriglyceridemias could be attributed to epsilon 4 allele. It is concluded that the genetic polymorphism of apoE modulates the effects of obesity on lipids and lipoproteins and that allele epsilon 4 increases the risk of obesity-induced hypertriglyceridemia.