A random sample of pulmonary and allergy subspecialists initially enrolled 600 persons with asthma identified in patient visit logs. This established panel completed 45 minute baseline and follow-up computer-assisted telephone interviews (CATI); 539 (90%) were successfully re-interviewed after 18 months of follow-up. A supplemental sampling frame of persons with asthma identified from family practitioners was completed as was a group with rhinitis but without asthma. Interviews assessed disease severity and other covariables using validated survey instruments. Pulmonary function and medical records were used to validate severity in a sub-sample of subjects. The study extended longitudinal follow-up study of this initial cohort. Its analysis tested predictive models for the asthma outcomes of interest.