Hospitalizations for acute exacerbation in patients with chronic obstructive pulmonary disease (COPD) have a great impact on health care expenditure. The aim of this study was to look at predictive factors of hospitalization for acute exacerbation in a group of patients with moderate to severe COPD. During the year 1994, we included 64 patients with COPD in this study. At inclusion, the patients being in a stable state, we performed a complete evaluation of their clinical, spirometric, gasometric, and pulmonary hemodynamic characteristics. All patients were followed during a period of at least 2.5 yr. We recorded the intervals free of hospitalization for exacerbation and realized an analysis of the proportional hazards not to be hospitalized using the Kaplan-Meier method. Univariate analysis using the log-rank test showed that the risk of being hospitalized was significantly increased in patients with COPD with a low body mass index (BMI <= 20 kg/m2, p = 0.015) and in patients with a limited 6-min walk distance (<= 367 m, p = 0. 045). But above all, the risk of hospitalization for acute exacerbation was significantly increased by gas exchange impairment and pulmonary hemodynamic worsening: PaO2 <= 65 mm Hg versus PaO2 > 65 mm Hg, p = 0.005; PaCO2 > 44 mm Hg versus PaCO2 <= 44 mm Hg, p = 0.005; and mean pulmonary artery pressure ( Ppa) at rest > 18 mm Hg versus Ppa <= 18 mm Hg, p = 0.0008. Neither age, nor the association of one or more comorbidities with COPD, nor the smoking habits had a significant impact on the risk of hospitalization in our study. Multivariate analysis showed that only PaCO2 and Ppa were independently related to the risk of hospitalization for acute exacerbation of COPD. We conclude that chronic hypercapnic respiratory insufficiency and pulmonary hypertension are predictive factors of hospitalization for acute exacerbation in COPD patients.