To characterize asthma in the elderly, 25 consecutive nonsmoking pulmonary clinic patients over the age of 70 who met the American Thoracic Society criteria for asthma were identified. Of these, 12 patients (48%) had developed asthma at an advanced age (greater than 65 yr). This group with late-onset asthma had a mean duration of disease of 5.1 +/- 2.5 yr. The remaining group with early-onset asthma had a mean duration of illness of 31.4 +/- 14.6 yr. On the day of evaluation each patient underwent pulmonary function testing off all medication for at least 12 h. These two groups were indistinguishable by symptoms and medication requirements. Immediate hypersensitivity skin testing to 43 aeroallergens was uniformly negative in all 25 patients but the histamine control was always positive. IgE levels in both groups were not different from those in elderly control subjects. Those with early-onset asthma had a greater likelihood of previous allergic disease (p less than 0.001) and a significantly greater degree of airflow obstruction in pre- and postbronchodilator pulmonary function testing (p less than 0.05). This study suggests that long-standing asthma may lead to chronic persistent airflow obstruction and thereby mimic chronic bronchitis and emphysema (COPD).