Our objective was to study the effects of candesartan on diabetic glomerulopathy in young normoalbuminuric and normotensive patients with type 1 diabetes in a double-blind, placebo-controlled trial. In 13 patients aged 24 years at baseline, we evaluated blood pressure, kidney biopsies and kidney function tests at baseline and after 5 years of treatment. Kidney biopsies were examined with light and electron microscopy, glomerular filtration rate and effective renal plasma flow determined with inulin and para-aminohippuric acid clearances. Two patients in the placebo group needed antihypertensive treatment because they developed microalbuminuria and/or hypertension, but no patient in the candesartan group did. A significant reduction in mesangial matrix volume and mesangial volume occurred in the candesartan group, although changes in morphological parameters were similar between groups. Office blood pressure was significantly lower in the candesartan group at follow-up than in the placebo group. Deterioration in morphological parameters observed in earlier studies of our patients did not become worse during treatment with candesartan or placebo. The effects of candesartan, with reduction in morphological parameters and lowering of blood pressure, might influence future treatment of glomerulopathy in type 1 diabetes patients.