Long-term (> or = 15 hours) oxygen therapy (LTOT) increases life-span and improves quality of life (QOL) in patients with chronic respiratory failure (CRF). However, in our clinical practice, we observed that very few patients are using oxygen therapy 15 hours or more. Furthermore, very few literatures about survival of non- or inadequate oxygen users were found. Thus, the aim of this study was to assess the effect of LTOT in patients with CRF. A total of 305 LTOT recommended patients with CRF in our clinic between 1996 and 2001 were found. A hundred and five patients with documented subject characteristics were included the study and followed-up approximately 20 months prospectively. They were divided into two groups whether to take LTOT (group 1, n= 71) or not (group 2, n= 34). Average life-span of the patients was 50 months in group 1 and 39 months in group 2 (p< 0.05). Survival (months) in group 1 was significantly correlated with hrs of oxygen use (r= 0.684, p= 0.001). One more hour oxygen use was statistically significantly correlated with 0.002 months more survival (F= 48.44, p< 0.05) in group 1 in logistic regression analysis. In comparisons, there were significant improvement in the post-treatment blood gas values in group 1 (p< 0.05). There were significant decreases in PFT values in the post-treatment period when compared to baseline values in both groups (p< 0.05). There was a less decrease in FEV(1) values per year in group 1 than group 2 but difference was not statistically significant (p> 0.05). In conclusion our findings revealed that LTOT provides improvement of the life-span of the patients with CRF.