We aimed to determine the prevalence of a prolonged QTc interval in HIV-infected patients and its related factors through an observational study of a cohort of asymptomatic HIV-infected outpatients. All patients underwent a standard 12-lead electrocardiogram and a transthoracic echocardiogram. Prolonged QTc was considered if it was >440 ms in men and >450 ms in women. Epidemiological, clinical, and laboratory data were collected and the patients completed a questionnaire about cardiovascular risk factors. The analysis of the potential risk factors for prolonged QTc was done by multivariate logistic regression. The study included 194 patients, 84% men, with a mean age of 46.3 years. The mean duration of HIV infection was 122.6 months and 27.8% had AIDS. Antiretroviral therapy was being taken by 185 (96.4%) patients, and 92.4% of them had an undetectable viral load. The mean CD4 lymphocyte count was 553/mm(3). A total of 24 (12.4%) patients had a prolonged QTc interval, with a mean QTc of 456 ms. The factors associated with a prolonged QTc were hyperlipidemia (OR 3.7, 95% CI: 1.3-10.3; p=0.01) and diastolic dysfunction (OR 6.7, 95% CI: 2.4-18.3; p=0.0001), while the use of atazanavir was associated with a lower likelihood of having a prolonged QTc (OR 0.11, 95% CI: 0.02-0.5; p=0.008). A prolonged QTc syndrome was not uncommon in this cohort of asymptomatic HIV-infected patients with good immunovirological control. It was associated with hyperlipidemia and diastolic dysfunction. The use of atazanavir, compared with other protease inhibitors, was associated with a lower likelihood of having a prolonged QTc.