OBJECTIVE: To examine factors that influence the natural history of asthma, such as genetics, atopy, air pollution and environmental tobacco smoke, gastroesophageal reflux, and infection, to promote early identification and treatment of patients at risk for persistent asthma. DATA SOURCES: Journal articles published in English involving human subjects with asthma. STUDY SELECTION: Studies were selected for their relevance to the discussion of asthma and the factors that contribute to its persistence. Epidemiologic studies were favored in assessing the natural history of asthma from childhood to adulthood. RESULTS: Major factors that can influence the severity and persistence of asthma are genetics, atopy, pollution, environmental tobacco smoke, gastroesophageal reflux, and respiratory infections. Epidemiologic studies reveal that factors strongly linked to the persistence of childhood asthma into adult life are early age of disease onset with more severe symptoms, atopy, and level of allergen exposure. CONCLUSIONS: Although there is still much research to be done, epidemiologic studies have repeatedly proven that the natural history of asthma is in some ways predictable. Early identification of patients at risk for persistent asthma, combined with early institution of pharmacologic and nonpharmacologic intervention strategies, may lead to better outcomes.