To examine the nature of asthma in the elderly, we compared older (group 1: 65 years or older, n = 50) with younger patients (group 2: <40 years, n = 99) and to determine the influence of long-standing disease, elderly asthmatics with early onset (group A: onset before 40, n = 22) were compared with patients developing symptoms later in their lives (group B: onset after 40, n = 22). Blood eosinophilia and IgE value greater than or equal to 100 IU/l were more frequent in younger patients. Short symptom-free periods were more frequent among older asthmatics (78.5 vs. 45.4%, p < 0.001). Only 31.2% of older patients had only mild symptoms. Requirement of systemic steroids was higher in the elderly population. The worst FEV1 was lower in older patients (54.4 +/- 17.3 vs. 71.8 +/- 18.5%, p less than or equal to 0.001). Patients with early-onset asthma showed more frequently shorter symptom-free periods (93.3 vs. 53.3%, p < 0.05), higher emergency admissions/year, and hospitalizations/year. Best FEV1 (group 1: 66.7 +/- 13.7% vs. group 2: 90.3 +/- 15.1%, p < 0.005) and worst FEV1 (46.2 +/- 13.1 vs. 61.0 +/- 13.2%, p < 0.01) were lower in early-onset patients. A higher systemic steroid requirement, a lower best and worst FEV1, shorter symptom-free periods and a lesser proportion of patients with only mild symptoms were observed in patients older than 65 with early-onset asthma compared with those younger than 40 years. Elderly patients with a shorter duration of asthma were not different from young patients. Our study strongly suggests that severity of asthma and development of irreversible airflow obstruction depend on the duration of disease.