BACKGROUND: Takotsubo syndrome (TTS) is characterized by transient left ventricular (LV) dysfunction and wall motion abnormalities without culprit coronary artery disease. LV thrombus (LVT) formation during the acute phase is a fearsome complication. OBJECTIVES: To identify factors associated with LVT and its prognostic impact in TTS patients. METHODS: Data from the nationwide REgistry on TAKOtsubo syndrome (RETAKO), which combines retrospective (2002-2012) and prospective (2012 onwards) recruitment with prospective follow-up, were reviewed to assess patient characteristics, imaging findings, and clinical outcomes according to the presence of LVT. RESULTS: Of 1478 TTS consecutive patients (median age 72 years, 13.5 % men), 42 patients (2.8 %) presented with LVT. Presentation with syncope, a typical "apical ballooning" pattern, the presence of late gadolinium enhancement (LGE) on cardiac magnetic resonance imaging, and elevated high sensitivity-C reactive protein (hs-CRP), were associated with LVT. On multivariable analysis, elevated hs-CRP at admission and LGE persisted as independent predictors of LV thrombus. Patients with LVT had higher rates of in-hospital major bleeding (9.5 % vs. 3.1 %, p = 0.023) and major adverse cardiovascular events (26.8 % vs. 15.2 %, p = 0.035), mainly driven by stroke (14.6 % vs. 2.5 %, p <
0.001) and systemic embolism (19 % vs. 1.3 %, p <
0.001). At a median follow-up of 18 months, there were no differences in mortality, cardiac readmissions, or TTS recurrence between groups. CONCLUSIONS: In TTS patients, elevated hs-CRP and LGE are associated with a higher risk of LVT. Although LVT is rare, it is associated with increased in-hospital thromboembolic events and bleeding, while long-term outcomes are comparable to those without LVT.