Sleep disordered breathing (SDB) is a frequent finding in the elderly. SDB is related to morbidity, mortality, quality of life, disability, and cognitive impairment. Treatment of choice for SDB is nasal positive airway pressure breathing (nCPAP). The impact of treatment for SDB on activities of daily living (ADLs) is unclear. We therefore investigated the relationship between SDB and ADLs in a sample of elderly in-hospital patients with severe SDB defined as a oxygen desaturation index of 30 events per hour. All patients eligible were assigned to nCPAP therapy. Patients with refusal of nCPAP were offered nocturnal oxygen supply via nasal prongs. The Barthel-index (BI) at admission and discharge was used to measure ADLs. Two hundred patients with a mean age of 81+/-7 years were included. 22 (11%) patients accepted nCPAP therapy, 42 (21%) patients accepted oxygen therapy and 136 (68%) patients refused both treatment options. The subgroups did not differ significantly in BI at admission and length of stay in hospital. BI increased from 42+/-28 to 49+/-30 in patients with refusal of any treatment, from 39+/-23 to 61+/-20 in patients with oxygen therapy and from 48+/-35 to 72+/-28 in patients with nCPAP therapy. The BI at discharge differed significantly between all three patients groups (p< 0.03). Logistic regression analysis revealed that Barthel Index at admission and treatment with nCPAP or treatment with oxygen were independently associated with a gain in BI of at least 30 points. Age, dementia or length of in-hospital stay showed no association with gain in BI. This is the first study that shows an impact of treatment for severe SDB on ADLs in elderly patients. Furthermore, treatment with nCPAP and oxygen supply nearly had the same impact on ADLs. Since the higher rate of acceptance of oxygen therapy and the important impact of oxygen supply on BI, administration of oxygen seems to be a rational alternative in elderly subjects with severe sleep apnea and refusal of nCPAP.