Context End-stage renal disease (ESRD) is one of the most severe complications of type 1 diabetes. Yet, data on patients’ risk of developing ESRD are sparse. Objectives To estimate the long-term risk of developing ESRD and to assess how age at diagnosis of diabetes, time period of diagnosis, and sex affect the risk. Design, Setting, and Patients A cohort of all patients younger than 30 years diagnosed as having type 1 diabetes in Finland in 1965-1999 (n = 20 005) was identified from the Finnish Diabetes Register. The cohort was followed up from diagnosis of diabetes until development of ESRD (dialysis or kidney transplantation as identified from the Finnish Registry for Kidney Diseases), death, or end of follow-up on December 31, 2001. Main Outcome Measure Cumulative incidence of ESRD, accounting for death as a competing risk. Results The cohort was followed up for maximally 37 years, with a median of 16.7 years. During 346 851 person-years, 632 patients developed ESRD. The cumulative incidence of ESRD was 2.2% at 20 years and 7.8% at 30 years after diagnosis. The risk of developing ESRD was lowest in patients whose diagnosis occurred at younger than 5 years. The risk of ESRD was lower for patients diagnosed as having type 1 diabetes in later years. The risk did not differ significantly between sexes. Conclusions With regard to ESRD, the prognosis of type 1 diabetes has improved during the past 4 decades. Children diagnosed as having diabetes before age 5 years have the most favorable prognosis. Overall, incidence of ESRD appears to be lower than previously estimated.