BACKGROUND: Although chronic obstructive pulmonary disease (COPD) is rapidly increasing in women, knowledge is lacking concerning differences in relative mortality and causes of death in women as compared with men. We aimed to analyze differences in relative mortality and cause-specific mortality between men and women on long-term oxygen therapy (LTOT) for COPD. METHODS: Patients starting LTOT for COPD in Sweden between 1 January 1987 and 31 December 2004 were prospectively followed until termination of LTOT or through 31 December 2004. Causes of death according to the Swedish National Causes of Death Register were compared between the study group and the general Swedish population matched for age and sex, with the relative mortality expressed as standardised mortality rates (SMR). RESULTS: 7,646 patients, 4,033 women and 3,613 men, were followed for a median of 1.7 years (range 0-18.0). No patient was lost to follow up. A total of 5,448 patients, 2,745 women and 2,703 men died. Women had a higher standard mortality rate than men overall, SMR 12.0 (95% confidence interval (CI), 11.6-12.5) vs. 7.4 (95% CI, 7.1-7.6), for respiratory disease (SMR 129.0 (95% CI, 123.3-134.7) vs. 66.4 (95% CI, 63.5-69.4)), cancer (SMR 3.5 (95% CI, 3.0-3.9) vs. 2.2 (95% CI, 1.9-2.5)) and cardiovascular disease (SMR 3.7 (95% CI, 3.3-4.1) vs. 2.5 (95% CI, 2.3-2.7)). CONCLUSIONS: In severe chronic pulmonary disease treated with long-term oxygen, women have higher relative mortality than men both overall and for respiratory disease, as well as for cardiovascular disease and cancer.