Aims/hypothesis: The bone-related peptide osteoprotegerin is produced by vascular cells and is involved in the process of vascular calcification. The aim of this study was to investigate the predictive value of plasma levels of osteoprotegerin in relation to mortality, cardiovascular events and deterioration in kidney function in patients with type 1 diabetes. Methods: This prospective observational follow-up study included 397 type 1 diabetic patients with overt diabetic nephropathy (243 men; age [mean±SD] 42.1±10.6 years, duration of diabetes 28.3±9.9 years, GFR 67±28 ml min -1 1.73 m2) and a group of 176 patients with longstanding type 1 diabetes and persistent normoalbuminuria (105 men; age 42.6±9.7 years, duration of diabetes 27.6±8.3 years). Results: The median (range) follow-up period was 11.3 (0.0-12.9) years. Among patients with diabetic nephropathy, individuals with high osteoprotegerin levels (fourth quartile) had significantly higher all-cause mortality than patients with low levels (first quartile) (covariate-adjusted hazard ratio [HR] 3.00 [1.24-7.27]). High osteoprotegerin levels also predicted cardiovascular mortality (covariate-adjusted HR 4.88 [1.57-15.14]). Furthermore, patients with high osteoprotegerin levels had significantly higher risk of progression to end-stage renal disease than patients with low levels (covariate-adjusted HR 4.32 [1.45-12.87]). In addition, patients with high levels of plasma osteoprotegerin had an elevated rate of decline in GFR. Conclusions/interpretation: High levels of osteoprotegerin predict all-cause and cardiovascular mortality in patients with diabetic nephropathy. Furthermore, high levels of osteoprotegerin predict deterioration of kidney function towards end-stage renal disease.