Studies reporting increased asthma hospitalizations and mortality in the United States and abroad have heightened concern about the changing epidemiology of asthma. We studied 20-yr patterns of acute asthma care occurring at two large community hospitals among members of a large health maintenance organization. The presentation focuses on the conceptualization and operationalization of an "episode" of asthma care, defined as a collection of encounters (emergency room visits, urgency care visits, and hospital admissions) that cluster in time, as well as on changes in episode rates over time. We found a statistically significant increase in asthma episodes among boys younger than 5 yr of age that continued unabated from 1967 to 1987 despite a drop in asthma hospitalization rates starting in 1985. We hypothesize that this difference may reflect a change in emergency room management practices and not a true change in the underlying epidemiology of asthma. The concept of an episode of acute asthma care has not been studied in the literature and represents a potentially useful methodologic innovation. Particularly in the context of managed health care systems, studies of such episodes may be less sensitive than studies of hospital admissions to changes in the organization and delivery of acute asthma care, and thus may be better suited for studying changes in the epidemiology of asthma.