Background: Few European groups have published data on series of patients with idiopathic anaphylaxis., Objective: Our aim was to report on our experience with this entity in Spain., Methods: We conducted a two-part investigation. The first part was a descriptive cross-sectional study of 81 patients with idiopathic anaphylaxis, diagnosed between January 1990 and December 1995 in the allergy unit of the General Hospital of Albacete in Albacete, Spain. The second prong was a prospective, longitudinal study that evaluated the activity of the condition., Results: Female patients constituted 68% of the study group with idiopathic anaphylaxis; the mean age of the 81 patients was 30.0 +/- 17.3 years. The number of episodes of idiopathic anaphylaxis during the year of greatest frequency varied widely (median, 2; range, 1 to 130). The duration also varied considerably, with a range of 0.03 to 300 months (median, 2 years). Most patients entered the study in remission, and 93% of these patients remained in remission throughout the followup period. Only 9% of the patients had vascular involvement. Our series of patients with idiopathic anaphylaxis had a notable prevalence of atopic diseases (48%), food allergy (20%), and episodes of anaphylaxis with an identifiable cause (15%). In addition, a high frequency (58%) of idiopathic urticaria was noted; the urticaria was acute in 62% of the affected patients., Conclusions: Our series of patients with idiopathic anaphylaxis is similar to previously published series.