Augmented carbonyl and oxidative stress may contribute to vascular complications in diabetes. The aim of the present study was to investigate whether carbonyl and oxidative stress is augmented in young patients with type 1 diabetes at early clinical stages of the disease. Urine samples of 38 patients with type 1 diabetes (mean age [±SD]: 12.8±4.5 years, diabetes duration: 5.7±4.3 years) and those of 60 age-matched healthy controls were assayed for advanced glycation end products (AGEs), pentosidine and pyrraline, and markers of oxidative stress, 8-hydroxy-2'-deoxyguanosine (8-OHdG) and acrolein-lysine. Of these four markers, urinary concentrations of pentosidine, 8-OHdG and acrolein-lysine were significantly higher in the diabetic patients than in the healthy controls. For the patient group, pentosidine correlated significantly with pyrraline, 8-OHdG and acrolein-lysine, and pyrraline correlated significantly with acrolein-lysine. Urinary pentosidine, 8-OHdG and acrolein-lysine, but not pyrraline, correlated significantly with urinary albumin excretion. Patients with microalbuminuria (≥15mg/g Cr) showed significantly higher levels of all the four markers than did normoalbuminuric patients and control subjects. The present study indicates that augmentation of carbonyl stress, which is closely linked to oxidative stress, and resultant endothelial dysfunction may start early in the course of type 1 diabetes.