Purpose: Long QT syndrome (LQTS) is a rare heterogeneous syndrome that may be congenital or, more frequently, acquired (aLQTS). The real-world prevalence of acquired LQTS in the emergency department is unknown.  Methods: The aim of this study was to determine the prevalence of this syndrome in the emergency room and to identify risk factors. Electrocardiograms (ECG) of 5056 consecutively patients admitted in the ER of a tertiary hospital between January 28th and March 17th of 2020 were reviewed. All patients with aLQTS were included. Clinical data with a focus on QT prolonging drugs and clinical factors were recorded. Statistical comparison was made between the groups with and without corrected QT interval greater than 500ms (value that is considered severely increased).  Results: A total of 383 ECGs with prolonged QTc were recognized, corresponding to a prevalence of aLQTS at admission of 7.81%. Patients with aLQTS were more commonly men (53.3%) with an age of 73.49±14.79 years old and QTc interval of 505.3±32.4ms. Only 20,4% of these patients with aLQTS were symptomatic. No ventricular arrhythmias were recorded. Patients with QT interval greater than 500ms were more frequently female (59,5%; p<0.001) and were more frequently on QT prolonging drugs (77,3%; p=0.025). Main contributing factor was intake of antibiotics (OR 4.680) followed by female gender (OR 2.473) and antipsychotics (OR 1.925). Conclusions: aLQTS is particularly prevalent in the ER. Female patients on antibiotics and antipsychotics are at particularly high risk. Efforts must be made to avoid, detect and treat aLQTS as early as possible.