BACKGROUND: The objective of this study was to assess the impact of pubertal maturation on urinary albumin excretion rate (AER) and persistent microalbuminuria, and to identify possible factors affecting urinary AER in adolescents with Type 1 diabetes. METHODS: One hundred patients aged 9.1-19.0 years with a duration of diabetes of >2 years out of 138 eligible adolescents with Type 1 diabetes from an outpatient diabetes clinic participated in the study, together with 100 healthy controls. A timed overnight urine sample was collected in the hospital, where all the adolescents stayed for 22-24 h, and microalbuminuria was confirmed with at least one consecutive positive sample (AER 20-200 microg/min). RESULTS: The prevalence of persistent microalbuminuria was 6%. All the patients affected were girls: one prepubertal (T I), one in late puberty (T IV) and three postpubertal (T V). These patients had significantly higher HbA(1c) levels than did the normoalbuminuric girls with Type 1 diabetes. Neither duration of diabetes nor age differed significantly between the two groups. AER increased more conspicuously with pubertal maturation in the boys with Type 1 diabetes than in the control boys, while the girls with diabetes had significantly higher body mass index (BMI) and serum total and LDL cholesterol than did the control girls. HbA(1c) was independently associated with AER in a multiple regression model. Diastolic blood pressure (BP) was elevated in both girls and boys with Type 1 diabetes as compared with healthy adolescents, while no difference was observed between the patients with microalbuminuria and normoalbuminuria. CONCLUSIONS: Persistent microalbuminuria was mainly observed in late puberty and after puberty among adolescents with Type 1 diabetes. Female sex and poor metabolic control predispose such adolescents to this condition during pubertal maturation.