QT and P wave dispersion parameters can indicate abnormalities in autonomic nervous system and cardiac functioning.To determine QT and P wave dispersion in patients with major depressive disorder compared with healthy volunteers.Fifty newly diagnosed patients with major depressive disorder and 50 age- and sex-matched healthy volunteers underwent 12-lead electrocardiography. QT interval, QT dispersion, heart rate-corrected QT dispersion and P wave dispersions were calculated manually by a blinded specialist.Groups were comparable in terms of age, sex, body mass index, smoking status, metabolic diseases and left ventricular ejection fraction. The major depressive disorder group had significantly higher QT dispersion (58.5±9.9 versus 41.7±3.8; P<0.001), heart rate-corrected QT dispersion (62.5±10.0 versus 45.2±4.3; P<0.001) and P wave dispersion (46.9±4.8 versus 41.5±5.1; P<0.001).Increased QT dispersion, heart-rate corrected QT dispersion and P wave dispersion in major depressive disorder patients may be indicative of autonomic imbalance and increased risk of cardiac morbidity and mortality.