OBJECTIVE Mannan-binding lectin (MBL) is a complement-activating carbohydrate-recognizing molecule associated with diabetic nephropathy. MBL is associated with all-cause mortality in type 2 diabetes, but whether MBL is associated with mortality in type 1 diabetes remains unknown. We therefore aimed to investigate this. RESEARCH DESIGN AND METHODS We studied an existing 12-year prospective cohort with type 1 diabetes with 198 patients with diabetic nephropathy (121 men, age 41 years [95% CI 40-42], estimated glomerular filtration rate [EGFR] 67 mL/min/1.73m2 [95% CI 63-70]) and 174 normoalbuminuric patients (103 men, age 43 years [95% CI 41-44], EGFR 93 mL/min/1.73 m2 [95% CI 91-95]). Mortality rates were compared according to the concentrationdetermining MBL2 genotype or the MBL concentration. Patients were classified as having high or low MBL expression genotypes. The effect of MBL concentration was estimated by comparing patientswithMBL concentrations above or belowthemedian. RESULTS Ninety-eight patients died during follow-up. The unadjusted hazard ratio (HR) for all-cause mortality was 1.61 (95% CI 1.07-2.43) for patients with high MBL expression genotypes versus patients with low MBL expression genotypes (P = 0.023). All-cause mortality was higher in patients with MBL concentrations above the median than in patients with MBL concentrations below the median (unadjusted HR 1.90 [95% CI 1.26-2.87], P = 0.002). CONCLUSIONS High MBL expression genotypes and high MBL concentrations are both associated with increased mortality rates in type 1 diabetes compared with low MBL expression genotypes and low MBL concentrations.