On January 1, 1987, 560 patients (267 male) were registered as using long-term domiciliary oxygen therapy (LTO) in Sweden. The duration of LTO before this date varied between 10 days and 11 yrs. During a two-year follow-up 12 patients had their LTO withdrawn because they were no longer hypoxic. In 139 patients the arterial oxygen tension (PaO2) on breathing air was registered three times. In seventeen (12%) of these patients the PaO2 exceeded 7.5 kPa on all three control occasions. The two year actuarial survival in all patients was 57%. The two year actuarial survival was 77% in patients with kyphoscoliosis, 56% in patients with sequelae of tuberculosis, 54% in patients with chronic obstructive pulmonary disease (COPD) and 39% in patients with fibrosis. In COPD patients survival was predicted by age, sex, current smoking habits, arterial carbon dioxide tension (PacO2) when breathing oxygen and oral steroid medication. A poor Zubrod performance score was associated with a high mortality rate in all patient groups.