Type 2 diabetes mellitus (T2DM) is a risk factor for cardiac and renal complications; its effect on cardiorenal syndromes is unknown. In a French nationwide cohort of 5,123,193 patients hospitalized in 2012 with ≥5 years of follow-up, we assessed the effect of T2DM on cardiorenal syndrome (CRS) (using cardiorenal, renocardiac, and simultaneous subtypes) incidence and outcomes using 1:1 propensity matching. Among 4,605,236 adults without cardiorenal syndrome, 380,581 (8.5%) with T2DM were matched to 380,581 adults without T2DM. During follow-up, CRS occurred in 104,788 patients: simultaneous n = 25,225 (24.0%); cardiorenal n = 51,745 (49.4%); renocardiac n = 27,818 (26.5%). T2DM doubled the risk of incident CRS (1.30% versus 0.65%/year; adjusted hazard ratio (HR) for any cardiorenal syndrome: 2.14 95% confidence interval 2.10;2.19; renocardiac: 2.43 2.34;2.53; cardiorenal: 2.09 2.03;2.15; simultaneous: 1.94 1.86;2.03. Among the 26,396 adults with CRS in 2012, 11,355 (43.0%) had T2DM and were younger than non-diabetic adults (77.4 ± 9.5 versus 82.3 ± 10.0); 8,314 patients with T2DM were matched to 8,314 patients without. T2DM increased risk of: end-stage kidney disease, adjusted HR 1.50 1.39;1.62; myocardial infarction 1.35 1.19;1.53; cardiovascular death 1.20 1.13;1.27; heart failure 1.17 1.12;1.21; and all-cause death 1.09 1.06;1.13, but not ischemic stroke. Patients with T2DM represent almost half of patients with CRS and are younger than their non-diabetic counterparts. T2DM doubles the risk of CRS and increases the risk of death, cardiovascular outcome, and end-stage kidney disease but not ischemic stroke after CRS.