Precordial ST-segment depression in acute inferior infarction is well recognized, but few studies have evaluated ST-segment elevation in lateral precordial leads. The present study examined the clinical significance of ST-segment elevation in lead V6 in patients with acute Q-wave inferior myocardial infarction. We studied the initial electrocardiography of 125 consecutive patients with acute Q-wave inferior myocardial infarction admitted to hospital within 12 h of the onset of chest pain. They were classified into two groups: group 1 = 34 patients with ST-segment elevation in lead V6; group 2 = 91 patients with no ST-segment elevation in lead V6. Among the seven clinical variables examined, the number of left ventricular asynergic segments (P < 0.001) and pulmonary capillary wedge pressure (P = 0.001) were related to ST-segment elevation in lead V6. The incidences of major arrhythmias (50% compared with 31%, P = 0.04), pericardial effusion (32% compared with 9%, P = 0.003), and pericardial rub (15% compared with 2%, P = 0.02) during the patients' stay in hospital were greater in group 1 than in group 2. Among the patients in group 1, the right coronary artery was the culprit artery in 22 of 24 patients (92%) with ST segment depression in lead I, whereas the circumflex artery was the culprit artery in nine of 10 patients (90%) with isoelectric or ST-segment elevation in lead I. The presence of ST-segment elevation in lead V6 in patients with acute Q-wave inferior myocardial infarction was associated with larger infarct size, and greater incidences of major arrhythmias and pericardial involvement during the patient's stay in hospital.