Abstract Background There is little information about the incidence of anaphylaxis from all causes. Objective The objects of this study were (1) to estimate the incidence of anaphylaxis; (2) to explore the range of diagnoses attributed to an anaphylactic episode; and (3) to describe the clinical features of anaphylaxis. Methods The study population consisted of children and adolescents enrolled at a health maintenance organization. We identified potential episodes of anaphylaxis occurring between 1991 and 1997 from automated databases and reviewed the medical record to confirm the diagnosis. We reviewed all diagnoses specific for anaphylaxis (eg, ICD-9 995.0, anaphylactic shock) and sampled from among other related diagnoses (eg, ICD-9 995.3, allergy unspecified). Estimation of the incidence of provider-diagnosed anaphylaxis was based on cases confirmed from among the specific diagnosis codes. Description of the clinical features of anaphylaxis involved all confirmed cases regardless of diagnosis. Results We identified 67 episodes of anaphylaxis among children with diagnosis codes specific for anaphylaxis (10.5 episodes per 100,000 person-years). There was no increase in incidence over time. Review of samples of diagnoses not specific for anaphylaxis yielded an additional 18 episodes. Among all identified episodes (n = 85), mucocutaneous and respiratory manifestations were the most common. Seventy-one percent of episodes were treated in the emergency department. Nine episodes (11%) resulted in hospitalization. Conclusions The incidence of anaphylaxis did not increase during these years. A majority of episodes were treated in the emergency department. Anaphylaxis in this population was frequently diagnosed as another related condition, and the basis and implications of diagnostic practices in this disorder warrant further exploration.