To determine the causes, risk factors and complications of planned extubation failure of critically ill elderly patients, we conducted a prospective study of 175 consecutive patients (> or = 70 years old) admitted with respiratory failure. Thirty-six (21%) failed extubation within 72 h after planned extubation. Compared to a younger age group (< 70 years old) matched for severity of illness, inability to handle secretions (20%) was the most common reason of airway causes leading to extubation failure in the elderly while upper airway obstruction (22%) was the predominant cause in the control group. As for nonairway causes, COPD related hypercapnic respiratory failure accounted for the majority of cases in both groups. After adjusting for severity of illness, elderly patients who required reintubation had a higher risk of developing nosocomial pneumonia. The presence of underlying pulmonary disease (odds ratio (OR), 2.9; 95% confidence interval (CI) 1.2-6.9), length of intubation > 4 days (OR, 4.3; 95% CI 1.8-10.2), and albumin levels < 2.5 g/dl (OR, 2.7; 95% CI 1.2-6.7) were independently associated with extubation failure in the old. Objective measurements of cough strength and secretion volume are needed to reduce the morbidity of elderly patients at risk for extubation failure.