BACKGROUND: The difficulty of implementing guidelines for long-term oxygen therapy (LTOT) has been recognized. We performed this analysis to evaluate the impact of a national quality assurance register on the quality of LTOT and to suggest indicators with levels for excellent quality LTOT. METHODS: Based on national register data on Swedish LTOT patients in 1987-2005, we measured nine quality indicators and the achievement levels of the participating counties in fulfilling these treatment criteria. RESULTS: There were improvements in the following eight quality indicators: access to LTOT, PaO(2) 16 h of oxygen/day, mobile oxygen equipment, reassessment of hypoxemia when LTOT was not started in a stable state of chronic obstructive pulmonary disease (COPD) and avoidance of continuous oral glucocorticosteroids in COPD. There was decline in the quality indicator PaO(2) > 8 kPa on oxygen. After improvements, three criteria were fulfilled by > or = 80% of the counties in 2004-2005. CONCLUSIONS: We found improvements in eight of nine quality indicators. We suggest these indicators with levels for excellent quality for use in quality assurance of LTOT based on our results.