OBJECTIVE - Many guidelines recommend reduced consumption of salt in patients with type 1 diabetes, but it is unclear whether dietary sodium intake is associated with mortality and end-stage renal disease (ESRD). RESEARCH DESIGN AND METHODS - In a nationwide multicenter study (the FinnDiane Study) between 1998 and 2002, 2,807 enrolled adults with type 1 diabetes without ESRD were prospectively followed. Baseline urinary sodium excretion was estimated on a 24-h urine collection. The predictors of all-cause mortality and ESRD were determined by Cox regression and competing risk modeling, respectively. RESULTS - The median follow-up for survival analyses was 10 years, during which 217 deaths were recorded (7.7%). Urinary sodium excretion was nonlinearly associated with all-cause mortality, such that individuals with the highest daily urinary sodium excretion, as well as the lowest excretion, had reduced survival. This association was independent age, sex, duration of diabetes, the presence and severity of chronic kidney disease (CKD) (estimated glomerular filtration rate [eGFR] and log albumin excretion rate), the presence of established cardiovascular disease, and systolic blood pressure. During follow-up, 126 patients developed ESRD (4.5%). Urinary sodium excretion was inversely associated with the cumulative incidence of ESRD, such that individuals with the lowest sodium excretion had the highest cumulative incidence of ESRD. CONCLUSIONS - In patients with type 1 diabetes, sodium was independently associated with all-causemortality and ESRD. Although we have not demonstrated causality, these findings support the calls for caution before applying salt restriction universally. Clinical trials must be performed in diabetic patients to formally test the utility/risk of sodium restriction in this setting.