OBJECTIVE In view of low prevalence rates, diabetes is discussed as a protective factor for the occurrence of Takotsubo syndrome (TTS). Furthermore, it was associated with improved outcome in a small single-center analysis. Therefore, this study assessed the prevalence and prognostic relevance of concomitant diabetes in TTS. RESEARCH DESIGN AND METHODS A total of 826 patients with TTS were enrolled in an international, multicenter, registry-based study (eight centers in Italy and Germany). All-cause mortality was compared between patients with diabetes and patients without diabetes, and the independent predictive value of diabetes was evaluated in multivariate regression analysis. RESULTS The prevalence of diabetes was 21.1% (n = 174). TTS patients with diabetes were older (P < 0.001), were more frequently male (P = 0.003), had a higher prevalence of hypertension (P < 0.001), physical triggers (P = 0.041), and typical apical ballooning (P = 0.010), had a lower left ventricular ejection fraction (P = 0.008), had a higher rate of pulmonary edema (P = 0.032), and had a longer hospital stay (P = 0.009). However, 28-day all-cause mortality did not differ between patients with diabetes and patients without diabetes (6.4% vs. 5.7%; hazard ratio [HR] 1.11 [95% CI 0.55–2.25]; P = 0.772). Longer-term follow-up after a median of 2.5 years revealed a significantly higher mortality among TTS patients with diabetes (31.4% vs. 16.5%; P < 0.001), and multivariate regression analysis identified diabetes as an independent predictor of adverse outcome (HR 1.66 [95% CI 1.16–2.39]; P = 0.006). CONCLUSIONS Diabetes is not uncommon in patients with TTS, is associated with increased longer-term mortality rates, and is an independent predictor of adverse outcome irrespective of additional risk factors.