BACKGROUND: Asthma in the elderly as well as asthma of adult-onset has been associated with increased morbidity, but little is known specifically about the effects of age on clinical and inflammatory outcomes in severe refractory asthma. The aims of the study were to examine the effects of age [lt;65 versus ?65 years] and age of onset of asthma [childhood-onset, lt;18 versus adult-onset, ?18 years] on clinical and inflammatory variables in patients with severe asthma. METHODS: In 1042 subjects with refractory asthma recruited to the British Thoracic Society Severe Asthma Registry, we compared patient demographics, disease characteristics and biomarkers of inflammation in patients aged lt;65 years (n = 896) versus ?65 years (n = 146) and onset at age lt;18 years (n = 430) versus ?18 years (n = 526). RESULTS: Severe asthma patients aged ?65 years had improved symptom control, better asthma quality of life and in the last year, less emergency visits and rescue oral steroid courses [3 (1-6) versus 5 (2-7), p lt; 0.001] than severe asthmatics aged lt;65 years. Blood eosinophils were lower in the elderly group. Patients with severe adult-onset asthma had similar symptom control, lung function and health-care utilization compared to severe childhood-onset asthma. Adult-onset asthmatics had higher blood eosinophils and were less atopic. CONCLUSIONS: Patients with severe refractory asthma aged ?65 years exhibit better clinical and health care outcomes and have lower blood eosinophils compared to those aged lt;65 years. Severe refractory adult-onset asthma is associated with similar levels of asthma control, higher blood eosinophils and less atopy than severe refractory childhood-onset asthma.