Previous trials, in which 76 to 100% of the patients were men, have shown a varied survival time in chronic obstructive pulmonary disease treated with long-term domiciliary oxygen therapy. We have analyzed predictors of survival in chronic obstructive pulmonary disease, including sex-related differences in survival in 403 patients (201 men) registered in a national register when starting long-term oxygen therapy between January 1, 1987 and June 30, 1989. This register covers the whole of Sweden with a population of 8.4 million. Some 90% of all the patients receiving long-term oxygen therapy are included. Lung function and performance status predicted survival during oxygen therapy in men, whereas a poor performance status and the presence of orally administered steroid medication predicted poor survival in women. Oral steroid medication use was correlated with an increased mortality rate in women (relative risk of death, 2.13; 95% confidence interval, 1.38 to 3.29; p < 0.001) and showed no tendency to improve survival in men. In patients not receiving oral steroids, women had a lower mortality rate than did men (relative risk of death, 0.58; 95% confidence interval, 0.39 to 0.97; p < 0.05). Our data indicate that in patients not receiving oral steroid medication, women have a better survival than do men. An increased mortality was found in women receiving oral steroid medication which might be caused by an increased susceptibility to the side effects of oral steroids.