Background: The cause for anaphylaxis cannot be identified after extensive evaluation in a large proportion of patients, who are classified as having ‘idiopathic anaphylaxis’ (IA). As food consumption patterns, genetic background, and environmental factors can lead to differences in allergen sensitization patterns in different regions, we sought to identify the aetiology of IA in cohort of Sri Lankan patients. Methods: Of the patients referred to our clinic following anaphylaxis, 65 were recruited as a cause could not be identified. The events that led to the episode of anaphylaxis, the triggers, the severity of symptoms and treatment received were recorded and skin prick test, ISAC ImmunoCAP test and serum tryptase was carried out. Results: Of the 65 patients, 42/65 (64.6%) were females and 49/65 (75.38%) were adults. 46/65 (70.8%) had grade II anaphylaxis and 34/65 (52.3%) were found to have specific IgE to alpha-gal, with symptoms occurring 0.5 to 6 hours since ingestion of food. Of those who had specific IgE to alpha-gal, 12 (35.3%) had consumed red meat and 10 (29.4%) milk products (3 had consumed fermented buffalo milk), before the episode of anaphylaxis. Difficulty in breathing, swelling of lips and syncope was significantly higher in those who were not sensitized to alpha-gal, while diarrhoea and abdominal pain were more common in those sensitized to alpha-gal, although this was not significant. Conclusion: A large proportion of patients presenting with IA were found to be sensitized to alpha-gal, which was the likely cause of their anaphylaxis.