The objective was to study the natural history and the predictive value of glomerular filtration rate, albumin excretion rate, blood pressure, and hemoglobin A1c for diabetic nephropathy. A cohort of 75 type-1 diabetic adolescents with a diabetes duration of 8 years was studied. Thirty-one females, 33 males, mean age 16.9 +/- 0.3 (SEM) participated in the follow-up study. Glomerular filtration rate, albumin excretion rate, blood pressure, and hemoglobin A1c were measured every second year during 8 years to determine the predictive value of glomerular filtration rate for future nephropathy. Initial differences and patterns of changes in glomerular filtration rate, albumin excretion rate, and hemoglobin A1c were examined in patients who did (group 1) and did not (group 2) develop incipient or overt nephropathy. Five of 64 patients developed overt nephropathy. They had an initial glomerular filtration rate of greater than 125 ml/min/1.73 m2. Fifteen of 53 initially normoalbuminuric patients developed incipient and three of 53 overt nephropathy. Age, age at onset, diabetes duration, initial albumin excretion rate, initial blood pressure, and hemoglobin A1c were similar in groups 1 and 2. Glomerular filtration rate was initially higher in group 1 than in group 2 (P = 0.01). The positive predictive value for combined incipient and overt nephropathy of an initial glomerular filtration rate greater than 125 ml/min was 53%. The negative predictive value of glomerular filtration rate less than 125 ml/min was 95%. In initially normoalbuminuric patients multiple regression revealed initial glomerular filtration rate as the only significant independent predictor for nephropathy when also corrected for hemoglobin A1c (P = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)