BACKGROUND Illicit drugs such as cocaine, and methadone can induce acquired long QT syndrome. OBJECTIVE The aim of this study was to evaluate the prevalence of cardiovascular disease and to assess the risk of torsades de pointes in substance abuse patients either with methadone or buprenorphine maintenance therapy, or without any specific therapy for opiate addiction. METHODS From November 2008 to December 2009, 190 patients (153 men, mean age 38.2 years, 22-56 years) with a substance use disorder according to DSM IV TR criteria were included in the study. All patients underwent blood tests, serial electrocardiogram (ECG) and, when necessary, additional testing, including echocardiogram, exercise test and Holter monitoring. Age and sex-matched healthy controls were also evaluated and compared with the cases. RESULTS One hundred and twenty-five patients (65.7%) had associated diseases. The prevalence of coronary artery disease and hypertension was, respectively, 2.1 and 5.2% in the addicted population. The percentage of abnormal ECGs was 34.2% in the addicted population and 4.7% in the nonaddicted population (P < 0.001). Twenty-five addicted patients had a QT interval prolongation (10 patients ≥ 480 ms). There were no sudden deaths or major cardiac events during the observation period. CONCLUSIONS Our results indicate that the QT interval prolongation is not a negative prognostic marker in the addicted population, even with associated diseases. ECG should be performed when other drugs potentially prolonging QT interval are associated. Substance abuse patients should be followed by multidisciplinary teams, and blood tests and ECGs should be performed regularly.