Asthma is defined as an obstructive disease of the pulmonary airways resulting from spasm of airway muscle, increased mucus secretion, and inflammation. The airways of asthmatic individuals are hyperresponsive to a variety of stimuli including cold air, atmospheric irritants, pharmacologically active chemicals, various drugs, and hyperventilation. The fundamental abnormality underlying the hyperresponsiveness appears to be genetically determined; two theories explaining the abnormality have received the most attention. One theory suggests that asthma is due to abnormal beta-adrenergic receptor-adenylate cyclase function with decreased adrenergic responsiveness. An alternate theory proposes that increased cholinergic activity in the airway is the fundamental defect in the disease. The true prevalence of asthma has been difficult to determine owing to uncertainties regarding the definition of the disease. Prevalence in various populations of children ranged from 1.37% to 11.4% or higher. Most studies report a preponderance of asthma in boys over girls, with ratios varying from 1.3:1 to 3.3:1. Risk factors for the disease include a history of atopy, acute lower respiratory tract disease, parental cigarette smoking, and bronchiolitis or croup. The spectrum of asthma is that of an illness beginning early in life and persisting, in some cases, through adulthood. Signs of the disease may be apparent in the first 2 yr of life and are often associated with viral respiratory infections. Disproportionate narrowing of peripheral airways and decreased static elastic recoil properties of the lung predispose infants and young children to asthma. During midchildhood there is a tendency toward improvement, with continued improvement during adolescence. The goal of management of the child with asthma is to reduce symptoms sufficiently so that the child can regularly attend school, engage in play activities, and sleep through the night uninterrupted, while avoiding unacceptable levels of adverse drug effects. Nonpharmacologic management includes both avoidance of environmental irritants and behavioral approaches to overcome emotional precipitants that lead to attacks. Pharmacologic treatment includes the use of four classes of drugs: (1) adrenergics, (2) theophylline, (3) cromolyn, and (4) corticosteroids. The prognosis of asthma in childhood is good. Although airway activity may remain abnormal for indefinite periods of time, most children reach a state where they are virtually free of symptoms.