OBJECTIVES: To develop a questionnaire to measure the additional social costs of food allergies (FAs). DATA SOURCE AND STUDY SETTING: People with FAs and sampled members of the general population (with and without FAs) in the Netherlands and the United Kingdom in 2006. STUDY DESIGN: (1) Literature review. (2) Focus group to identify key costs of FAs and seek views on the questionnaires. (3) Pilot survey to test the questionnaires in cases and controls. DATA COLLECTION: Twenty-eight participants in the United Kingdom and the Netherlands with clinically or self-diagnosed FAs took part in one of five focus groups. A case-control postal survey was conducted in the United Kingdom and the Netherlands (with 125 FA cases and 62 controls). PRINCIPAL FINDINGS: Methods exist to measure social costs in chronic illness, but not FAs. Focus groups found features of FAs likely to impact costs of living. Pilot results suggest higher costs of living and health care costs, and well-being in FAs. CONCLUSION: The questionnaire is proposed for use in wider European and other comparative studies of FAs.