OBJECTIVE - To analyze the changes in glomerular filtration rate (GFR), urinary albumin excretion rate (UAER), and blood pressure (BP) levels in a cohort of normoalbuminuric and normotensive type 1 diabetic patients. RESEARCH DESIGN AND METHODS - This is an 8.4 ± 2.1-year prospective study of 33 normotensive normoalbuminuric (24-h UAER <20 μg/min) type 1 diabetic patients. UAER (radioimmunoassay), GFR (51Cr-EDTA single-injection technique), and GHb (ion-exchange chromatography) were measured at baseline and at 1- to 2-year intervals. RESULTS - The GFR decreased (137.6 ± 16.5 to 116.4 ± 21.3 ml · min-1 · 1.73 m-2 P < 0.05) during the follow-up period. GFR reduction (-0.20 ± 0.29 ml · min-1 · month-1; P < 0.05) was associated with baseline GFR and mean GHb (R2 = 0.30; β = 0.072; F = 6.54; P = 0.004). UAER was higher at the end of the study (3.7-7.1 μg/min; P = 0.017). Microalbuminuria was observed in two patients, while macroalbuminuria was observed in one. No changes in UAER were observed when these three patients were excluded from the analysis. Mean blood pressure (MBP) increased during the study (85.8 ± 9.7 to 99.6 ± 11.6 mmHg; P <0.001). MBP at the end of the study was associated with age and GFR at baseline (R2 = 0.39; β = 0.074; F = 9.64; P = 0.001). CONCLUSIONS - In this cohort of normoalbuminuric normotensive type 1 diabetic patients, GFR decreased and BP levels increased during the follow-up period. The predictors for the GFR change were baseline GFR level and metabolic control. For end-of- study MBP, the predictor was baseline GFR level.