OBJECTIVE: Patients with type 1 diabetes (T1D) have a higher risk of developing chronic kidney disease, cardiovascular events (CVEs), and mortality than the general population. We hypothesized that two previously published biomarkers, namely PRO-C6, a biomarker of collagen type VI formation, and C3M, a biomarker of collagen type III degradation, may be associated with impaired renal function and have prognostic value for adverse renal, CVE, and mortality in patients with T1D. RESEARCH DESIGN AND METHODS: PRO-C6 and C3M in serum (sPRO-C6, sC3M) and urine (uPRO-C6, uC3M) were measured by ELISA in 663 patients with T1D ranging from normoalbuminuric to macroalbuminuric. Association of the biomarkers with mortality, CVEs, heart failure, decline in estimated glomerular filtration rate (eGFR) ≥30%, and end-stage renal disease (ESRD) were tested in Cox proportional hazards models after log transformation and adjusted for relevant clinical characteristics. Hazard ratios (HRs) were reported per doubling of biomarker levels. RESULTS: High levels of sPRO-C6 were independently associated with a higher risk of all-cause mortality (HR 2.26 [95% CI 1.31-3.87], < 0.0031). There was an association with higher risk of CVEs ( = 94) and heart failure ( = 28) but not after adjustment ( ≥ 0.58). In relation to renal outcomes, adjusted sPRO-C6 was associated with a higher risk of eGFR decline ≥30% in T1D, with eGFR >45 and >30 mL/min/1.73 m, and with a higher risk of ESRD (all ≤ 0.03). Higher uPRO-C6 was associated with a lower risk of decline in eGFR. CONCLUSIONS: In patients with T1D, higher sPRO-C6 was an independent predictor of both decline in eGFR and development of ESRD and of all-cause mortality. Higher uPRO-C6 was also associated with a lower risk of decline in eGFR.