This study was conducted to determine whether changes in the levels of plasma apolipoproteins (apo) AI, A-II, B, C-II, and C-III, along with cholesterol and triglycerides, could provide additional information on these parameters in relation to the control of glycemia. Plasma and lipoprotein lipids and apolipoprotein levels were measured in 123 insulin-dependent diabetic children (4-to 12-years-old), classified into good, fair, and poor diabetic control based on HbA1c and fructosamine levels, and in 62 comparable healthy controls. Total cholesterol, very low density lipoprotein cholesterol, and low density lipoprotein cholesterol, as well as total triglycerides, very low density lipoprotein, low density lipoprotein, and high density lipoprotein (HDL) triglycerides, and apo B and apo C-III were increased significantly in children with fair and poor diabetic control. While in diabetic children with good control, only very low density lipoprotein cholesterol was elevated significantly compared with healthy control subjects. Conversely, the levels of cholesterol in HDL, HDL2, HDL3, and apo AI were decreased significantly in the three diabetic groups, but apo A-II and apo C-II did not change. We conclude that in children with insulin-dependent diabetes mellitus, abnormalities in plasma lipid, lipoprotein, and apolipoprotein levels occur, the extent of which depends on the degree (extent) of glycemic control (the poorer the control the more substantial the abnormality). We suggest that measurement of apo C-III level along with apo B and apo AI in these patients may be a sensitive indicator to alterations in glycemic control.