Malondialdehyde, a marker of lipid peroxidation, was measured as thiobarbituric acid reactive substances (TBARS) in 117 diabetic patients and 53 controls. Patients were divided into groups and subgroups according to the type of diabetes (type 1 and type 2) and the existence or not of vascular complication (macro- or micro-angiopathy). Results showed that TBARS concentrations were significantly higher in type 1 (P < 0.0001) and type 2 (P < 0.001) diabetic patients than in the control group. The plasma TBARS concentrations in type 1 and type 2 diabetic patients did not differ significantly. Among the patients with vascular disease, type 2 diabetic patients with macroangiopathy had significantly higher TBARS concentrations than patients with no vascular complication (P < 0.05). Whichever the type of diabetes, there was no correlation between TBARS concentrations and glycaemic control: glycosylated haemoglobin, fasting blood glucose. This study confirmed the existence of lipid peroxidation disorders in diabetic patients.