OBJECTIVE To examine the clinical significance of precordial ST-segment changes in patients with acute Q-wave inferior wall myocardial infarction. METHODS Prospective evaluation (clinical follow-up) of Q-wave inferior wall myocardial infarction over a 6-year period in patients who fulfilled the inclusion criteria. METHODS Coronary care unit at a university hospital. METHODS Two hundred consecutive patients with acute Q-wave inferior wall myocardial infarction admitted to the coronary care unit within 24 h from the onset of chest pain. RESULTS Precordial ST-segment depression resolved <24 h (transient) after admission in 84 patients, lasted > or = 24 h (persistent) in 48 patients, and was absent in 68 patients, while ST-segment elevation in V4R was detected in 60 patients. Seventy-one patients had major in-hospital complications and 18 patients died in the hospital. When nine variables were used in the multivariate analysis, right ventricular dilatation and persistent precordial ST-segment depression were the important factors related to major in-hospital complications, whereas age, alveolar arterial oxygen difference, and persistent precordial ST-segment depression were important for in-hospital deaths. CONCLUSIONS Left ventricular posterior wall involvement, diagnosed by persistent precordial ST-depression, was an independent and stronger predictor of major in-hospital complications and deaths than right ventricular involvement in patients with acute Q-wave inferior wall myocardial infarction.