The purpose of the present study is to elucidate the characteristics of lipoprotein disorders in diabetes mellitus. By analytical ultracentrifugation, non-insulin-dependent diabetic patients (NIDDM) with type IIa hyperlipoproteinemia (HLP) showed significantly higher incidence of multidisperse low density lipoprotein (LDL) than non-diabetics with type IIa HLP. Furthermore, LDL multidispersity in diabetic subjects seemed to be directly related to neither triglyceride (TG) levels in very low density lipoprotein (VLDL) nor the degree of glycemic control. Diabetics with multidisperse LDL had a lipoprotein profile that was different from the subjects with paucidisperse LDL as follows: (1) enrichment in the cholesterol content of VLDL, (2) TG-rich LDL with small flotation coefficient, (3) low cholesterol levels in high density lipoprotein2 along with enrichment in TG, and (4) high plasma concentrations of apoprotein B. Although the underlying mechanism behind the prevalence of multidisperse LDL in NIDDM with type IIa HLP remains unknown, it seems important that lipoprotein disorders in diabetics with multidisperse LDL were potentially atherogenic.