OBJECTIVES: The quality-adjusted life expectancy (QALE) and loss of quality-adjusted life expectancy (loss of QALE) in patients under prolonged mechanical ventilation (PMV) stratified by different underlying diseases were determined. METHODS:  A simple random sample of all 171, 635 patients who were performed continual mechanical ventilation for more than 21 days during the 1997-2007 periods in Taiwan left us 50,481 subjects. After stratifying the patients according to specific diagnoses, we performed latent class analysis (LCA) to categorize PMV patients with multiple comorbidities into several clustered groups. The survival functions were estimated for each group with Kaplan-Meier method and extrapolated to 300 months to obtain the life expectancies through a semi-parametric method. The results were adjusted with a utility measurement of quality of life to estimate the QALE (quality-adjusted life expectancies). Further, we compared the age-, gender-matched reference populations to calculate the loss of QALE. RESULTS: The QALE of PMV patients with chronic renal failure were 0.42 and 0.19 quality-adjusted life years (QALY) for consciousness clear versus unclear states, respectively; those of patients with cancer were 0.48 and 0.22, respectively; those of patients with Parkinson’s disease were 0.62 and 0.27, respectively; those of patients with liver cirrhosis were 0.98 and 0.43 respectively; those of patients with stroke were1.03 and 0.46 respectively; those of patients with degenerative neurological diseases were 1.47and 0.64 respectively; those of patients with injuries and poisoning were1.81 and 0.78 respectively . The LCA classified cases with multiple comorbidities into several categories, of which there was a consistent trend of decrease in QALE and loss of QALE as people grow old. CONCLUSIONS: The results could hopefully reduce the gap between patients’ families and health care providers and assist the clinical and health policy decisions.