Possible association between several variables and the prognosis of nephropathy was investigated in 23 insulin-dependent diabetics with established diabetic nephropathy. Age at onset and duration of diabetes, blood pressure and metabolic control were among these variables. In the mean observation period of 27 months, end-stage renal disease (ESRD) developed in 11 patients. Nine patients died, including six with progression to ESRD, mainly of cardiac disease. Age, duration of diabetes, insulin requirement, blood pressure and glycosylated hemoglobin concentration showed higher values in the patients with progression to ESRD, but no difference was statistically significant. During the observation time, however, blood pressure was less well controlled in the patients who developed ESRD. The deterioration rate of renal function showed wide interindividual variation. In each patient, however, the decline seemed to follow a linear regression course. The results suggest that, in the absence of dependable prognostic factors, regular individual monitoring of glomerular filtration rate can provide a reliable predictive estimate of the progression rate.