The aim of this study was to evaluate serum advanced glycation end products (S-AGEs) in a group of adolescents and young adults with type 1 (insulin-dependent) diabetes mellitus and with diabetic microvascular complications (nephropathy or retinopathy). Fifty-two patients were included in the study (age range 14.2-28.8 years, onset of diabetes before the age of 12 years, duration of diabetes longer than 7 years); 45 patients without diabetic angiopathy and 63 healthy controls were also selected. S-AGEs were significantly increased in patients with diabetic angiopathy compared with controls (19.9+/-3.8 vs. 11.8+/-2.8 U/ml, P<0.001). Higher S-AGE levels were found in patients with severe diabetic nephropathy and retinopathy. When the albumin excretion rate (AER) was >100 microg/min per 1.73 m2, S-AGE levels were 23.1+/-2.4 U/ml; when the AER was 50-100 microg/min per 1.73 m2 levels were 19.8+/-1.9 U/ml, and for an AER of 20-50 microg/min per 1.73 m2 the corresponding value was 16.1+/-2.1 U/ml (P<0.005). Patients with proliferative retinopathy had S-AGE levels of 22.2+/-2.6 U/ml, those with preproliferative retinopathy 20.7+/-2.2 U/ml, and background retinopathy 17.6+/-1.9 U/ml (P<0.01). A significant correlation was found between levels of glycosylated hemoglobin (HbA1c) and S-AGE (r=0.43, P<0.01). S-AGE concentrations are markedly increased in type 1 diabetic adolescents and young adults with diabetic nephropathy and retinopathy. The severity of diabetic angiopathy is related to the serum levels of AGEs.