OBJECTIVES: The aims of the Online Latin American Survey of Anaphylaxis (OLASA) were to identify the main clinical manifestations, triggers, and treatments of severe allergic reactions in patients who were seen by allergists from July 2008 to June 2010 in 15 Latin American countries and Portugal (n =634). RESULTS: Of all patients, 68.5% were older than 18 years, 41.6% were male, and 65.4% experienced the allergic reaction at home. The etiologic agent was identified in 87.4% of cases and predominantly consisted of drugs (31.2%), foods (23.3%), and insect stings (14.9%). The main symptom categories observed during the acute episodes were cutaneous (94.0%) and respiratory (79.0%). The majority of patients (71.6%) were treated initially by a physician (office/emergency room) within the first hour after the reaction occurred (60.2%), and 43.5% recovered in the first hour after treatment. Most patients were treated in an emergency setting, but only 37.3% received parenteral epinephrine alone or associated with other medication. However, 80.5% and 70.2% were treated with corticosteroids or antihistamines (alone or in association), respectively. A total of 12.9% of the patients underwent reanimation maneuvers, and 15.2% were hospitalized. Only 5.8% of the patients returned to the emergency room after discharge, with 21.7% returning in the first 6 hours after initial treatment. CONCLUSION: The main clinical manifestations of severe allergic reactions were cutaneous. The etiologic agents that were identified as causing these acute episodes differed according to age group. Following in order: drugs (31.2%), foods (23.3% and insect stings (14.9%) in adults with foods predominance in children. Treatment provided for acute anaphylactic reactions was not appropriate. It is necessary to improve educational programs in order to enhance the knowledge on this potentially fatal emergency.