The SIDRIA project (Italian Studies on Respiratory Disorders in Children and the Environment) is aimed at evaluating the prevalence of respiratory and allergic disorders, and their geographic and temporal variations, in the context of the ISAAC study (International study of asthma and allergies in Childhood). The SIDRIA study was specifically designed to evaluate the prevalence of a variety of environmental, social, behavioural and familiar risk factors, and to examine the association between these socio-environmental factors and asthma as well as other respiratory disorders in children. The first phase of SIDRIA was conducted in 1994-1995 in 10 areas of Northern and Central Italy. The 2nd phase took place in 2002, in 13 Italian areas, and included 20,016 children (6-7 years old) and 16,175 adolescents (13-14 years old), with a response rate of 89% and 93%, respectively.