Asthma, hay fever and eczema are three common chronic conditions. There have been no recent multi-country data on the burden of these three conditions in adults; the aims of this study are to fill this evidence gap. The Global Asthma Network Phase I is a multi-country cross-sectional population-based study using the same core methodology as the International Study of Asthma and Allergies in Childhood Phase III. It provides data on the burden of asthma, hay fever and eczema in children and adolescents, and, for the first time, in their parents/guardians.