Purpose: To determine the effect of invasive mechanical ventilation on morbidity and mortality rate in patients with chronic obstructive pulmonary diseases (COPD). Patients and Methods: This study was carried out between January 1997 and March 1999, in the Medical Intensive Care Unit of Erciyes University Medical School, Kayseri. Thirty-four patients were included in the study; twenty-four patients were male and ten were female. The median age was 64 (39-78) years. Results: Indications for mechanical ventilation were cardio-pulmonary arrest in eleven patients, cerebrovascular accident (CVA) in two patients, and acute pulmonary failure in twenty-one patients. Twenty patients (59%) died during therapy. Causes of death were heart failure (7 cases), sepsis (5 cases), CVA (3 cases), pulmonary failure (3 cases), leukemia (1 case), and hyperosmolar coma. There was not any underlying disease in patients who were weaned from the mechanical ventilator. Intermittent mechanical ventilation were applied to ten patient and nine of them recovered from respiratory failure. Conclusion: In conclusion, the prognosis of COPD is poor in patients if there is an underlying disease however, mechanical ventilation is successful in only selected patients.