To learn how differences among individual patients influence the outcomes of their emergency room (ER) visits for asthma, we matched the results of 1209 sequential ER visits with the records of the 464 children and young adults who visited during a 37-week interval. Most patients visited the ER only once and were unlikely to be admitted. Those patients admitted once were unlikely to be admitted a second time. Only 119 patients (25.6%) made 54.7% of all ER visits and were responsible for 68.5% of admissions; they also accounted for all but eight of 92 relapses. Patients were accordingly stratified into group F, frequent visitors, and group I, infrequent visitors. A separate high-risk category (group HR) was composed of 50 other patients who received especially conservative treatment in the ER owing to prior episodes of severe asthma. HR patients included both frequent and infrequent visitors and had a very high probability of being admitted on any given visit. The patients of group F, each of whom visited the ER at least four times during the 37 weeks initially studied, were also consistently frequent visitors for comparable periods before and after the initial period. Their rate of ER relapses for exceeded their visiting rate, at least in part because some patients tended to relapse on repeated occasions. Patterns of ER use allow differentiation among groups of patients with distinctly different prognoses. These groups are similar to prognostic categories reported by previous authors. Such differences among individual patients must be taken into account when management systems are evaluated or clinical strategies are organized.