Current knowledge about the epidemiology and natural history of childhood asthma is incomplete, but the relationship between asthma early in life and development of chronic obstructive pulmonary disease (COPD) in adulthood is becoming more apparent. Asthmatic children with persistent and severe asthma symptoms have lower levels of lung function by young adulthood than those with milder disease. Recent longitudinal studies have confirmed a decrease in rate of growth of lung function as measured by FEV1 among symptomatic (primarily wheeze) children compared to asymptomatic children. Among persons who develop COPD, initial level of lung function is the strongest predictor of subsequent rapid decline of ventilatory function.