The benefits of long-term oxygen therapy (LTOT) on mood in Chronic Obstructive Pulmonary Disease (COPD) are unproven. Longitudinal studies are affected by disease progression, the increased package of care (with LTOT) and may not control for known confounders on mood. We compared the point prevalence and severity of mood disturbance in patients with severe COPD, not on LTOT (the -LTOT group) to those with COPD on LTOT (the +LTOT group). We mailed the Hospital Anxiety and Depression (HAD) Score to 182 consecutive patients with severe COPD, identified from respiratory case notes in three UK Hospitals. We compared 57 patients not prescribed LTOT to 57 patients on LTOT, and used stratified sampling to match the groups as far as possible for age, gender, lung function and other possible confounders on mood. Or these, 25% of patients in both groups scored in the 'definite' case range for anxiety (HAD score >or= 11). 37% of the -LTOT group and 33% of the +LTOT group scored in the 'definite' range for depression (HAD score >or= 11) (p=N.S). In both groups, only 11% of responders were prescribed anxiolytics and/or antidepressants. Further multiregression analysis confirmed that socio-demographic variables (e.g., lives alone, feels isolated or recent life events) were stronger predictors of mood than the prescription of LTOT or other traditionally accepted factors such as co-morbidity or the use of antidepressants or anxiolytics. High levels of anxiety and depression are present in severe COPD and appear under-treated. The +LTOT and -LTOT patients had a similar high prevalence of anxiety and depression.