We examined 166 patients with advanced chronic obstructive pulmonary disease (COPD) treated with long-term oxygen therapy (LTOT) in order to evaluate the prognostic factors of such patients. The mean observation period was 24 months (range 2-50 months) and the following variables were considered: age, forced expiratory volume in 1 s (FEV1), arterial oxygen tension (PaO2), arterial carbon dioxide tension (PaCO2), hematocrit, right ventricular systolic pressure (RVSP; evaluated by Doppler echocardiography), number of hospitalizations in the 2 years prior to prescription of LTOT and body mass index. The overall survival rate was 78.3% at 24 months and 67.1% at 36 months. A univariate analysis identified three variables as significant predictors of survival: FEV1, PaO2 and RVSP. A multivariate analysis, using Cox's model, showed an independent predictive power for RVSP, age and FEV1. RVSP higher than 35 mm Hg, age greater than 70 years and FEV1 lower than 30% of the predicted value were associated with shortened survival. The importance of pulmonary hypertension as a predictor of death suggests that LTOT could be prescribed earlier for COPD patients with cor pulmonale, as oxygen has been shown to be the only effective therapy for improving the survival probability of these patients.