Overnight urinary albumin excretion (UAE) was measured in 51 patients, nine to 18 years old, with type 1 (insulin-dependent) diabetes mellitus and in 22 healthy subjects using radioimmunoassay. Thirteen diabetic patients (25.5%) had microalbuminuria defined as UAE rate between 20 and 200 microg/min. Eleven of these patients were over 13 years of age. This gives a frequency of microalbuminuria of 42% (11/26) in the diabetic children and adolescents in the age group 14-18 years. UAE rate was positively correlated with both age at diagnosis and duration of diabetes. Arterial blood pressure, systolic and diastolic, glycosylated hemoglobin (HbA1c) and insulin dosage U.kg- 1.day-1 were significantly higher (P<0.001) in the diabetic patients with microalbuminuria compared to the diabetic patients with normal UAE rate. Retinal changes were also more common in the microalbuminuric diabetic patients than in the diabetic patients without microalbuminuria (P<0.01). This study has revealed a high prevalence of microalbuminuria in young Sudanese patients with type 1 (insulin-dependent) diabetes mellitus and emphasized the importance of routine screening of diabetic children after the age of 12 years.