Introduction Drug-induced long QT syndrome (DI-LQTS) is a clinical entity with prevalence and arrhythmic risk not well defined. Purpose To determine the clinical characteristics of patients with DI-LQTS diagnosed in the setting of a tertiary hospital center. Methods Prospective observational study with consecutive inclusion of patients with the diagnosis of DI-LQTS as per standard criteria, in a tertiary hospital, between 2018 and 2022. Results Eighty-five patients were included (age 65±15 years, 59% male). The mean corrected QT interval (QTc) of the entire cohort was 545±56 ms. The drugs responsible for QTc prolongation were: psychotropic drugs 51%, antiarrhythmics 38%, anesthetics 29%, antibiotics 15%, antineoplastics 3%, other 2%. QTc prolongation was due to the combination of ≥2 responsible drugs in 46 (54%) patients, and to the use of a single drug in 39 (46%). Twenty-one patients (25%) presented ventricular arrhythmias at the time of drug-induced QT prolongation: 10 (12%) ventricular fibrillation, 7 (8%) sustained ventricular tachycardia, 3 (3%) non-sustained ventricular tachycardia, 1 (1%) frequent ventricular extrasystole. Patients with ventricular arrhythmias were older (73±12 vs 62±15 years, p<0.05) and exhibited longer QTc prolongation (600±59 vs 528±42 ms, p<0.05). Conclusion The DI-LQTS is a rare clinical entity but may be cause of clinically-relevant ventricular arrhythmias. Older age and greater prolongation of the QTc interval are associated with an increased risk of ventricular arrhythmic events. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Health Institute Carlos III, Spain