This study was designed to determine the prevalence of microalbuminuria and the associated risk factors in patients with childhood-onset diabetes mellitus (DM). One hundred and sixty-three patients (141 with type 1 DM [DM1] and 22 with type 2 DM [DM21), aged 8 to 28 years, were evaluated for albumin excretion rate and HbA(1c). The mean duration of DM was 8.1 +/- 3.4 and 5.5 +/- 3.9 years in DM1 and DM2, respectively. Persistent microalbuminuria and macroalbuminuria were observed in 11.3% and 2.8% of patients with DM1, and 18.2% and 4.5% in patients with DM2, respectively. In DM1, the duration of DM, age of onset, and HbA(1c) levels were significant predictors of microalbuminuria. Our observations suggest that screening for microalbuminuria should be started from early adolescence in patients with DM1 and DM2.