The adherence to entry criteria and results of one year long-term oxygen therapy (LTOT) in Poland were analysed. Four hundred and seven patients with advanced respiratory failure due to chronic lung diseases qualified for LTOT were observed for one year in 12 regional LTOT centres. There were 315 patients with chronic obstructive pulmonary disease (COPD) and 92 with other chronic lung diseases. In 270 patients the prescription of oxygen was based on the single criterion of stable arterial oxygen tension (PaO2) less than or equal to 55 mmHg (7.3 kPa); and in the remaining 137 with less severe stable hypoxaemia (PaO2 56-65 mmHg) (7.4-8.6 kPa), on concomitant signs of cor pulmonale and/or of tissue hypoxia. Of 407 patients who started LTOT, 95 (23%) died during the first year of treatment. The mortality rate was 21% for COPD patients and 33% for patients with other lung diseases. After one year of LTOT 312 patients survived: 250 COPD patients and 62 with other lung diseases. Of these, 19 COPD patients (8%) and 9 with other chronic lung disease (15%) who had PaO2 less than or equal to 55 mmHg (7.3 kPa) when oxygen was prescribed, presented with PaO2 greater than 55 mmHg (7.3 kPa). From the 137 patients (106 with COPD and 31 with other lung diseases) who qualified with less severe hypoxaemia, 10 COPD patients (10%) and 5 (16%) with other lung disease had PaO2 greater than 65 mmHg (8.6 kPa).(ABSTRACT TRUNCATED AT 250 WORDS)