Background: Impaired diastolic function is a hallmark of diabetic cardiomyopathy and a common feature in type 1 diabetes mellitus (T1DM). The ratio of transmitral early filling velocity to early diastolic strain rate (E/e'sr) has in recent studies proved to have strong prognostic value. This study aimed to investigate the prognostic value of E/e'sr compared to E/e’ in T1DM without known heart disease. Methods: In this prospective cohort of T1DM patients, echocardiography was performed including two-dimensional speckle tracking. Follow-up was performed using nationwide registries. Outcomes were all-cause mortality and major cardiovascular events (MACE). Results: In total 1079 patients (age: 49.6 ± 14.5 years, 52.5% male, duration of diabetes 25.8 ± 14.6 years) were included in the study. During follow-up (median 6.3 years, IQR:5.7–6.9) 13.2% experienced MACE and 5.8% died. Following multivariable adjustment, both E/e'sr and E/e’ was significantly associated with both MACE (E/e'sr: HR 1.16 CI95%:[1.05–1.29], p = 0.005, per 10 cm increase) vs. (E/e’: HR 1.09 CI95%:[1.03–1.15], p = 0.001, per 1 unit increase) and all-cause mortality (E/e'sr: HR 1.20 [1.03–1.40], p = 0.016) vs. (E/e’: HR: 1.11 [1.02–1.20], p = 0.016). Sex modified the association between E/e'sr and MACE (p for interaction = 0.008) such that E/e'sr after multivariable adjustment only remained significantly associated with MACE in females (HR: 1.41 [1.19–1.67], p < 0.001) but not in males (HR: 1.06 [0.93–1.20], p = 0.42). In females, E/e'sr provided incremental information beyond the Steno T1 Risk Engine (Harrell's C-statistic: 0.78 (0.72–0.83) vs. 0.81 (0.75–0.86), p = 0.007). Conclusion: In patients with T1DM, both E/e'sr and E/e’ provides independent prognostic information regarding prognosis. E/e'sr seems to have stronger prognostic value in females with T1DM.